feat(parser): Implement hosts file parser with intelligent formatting

- Added `internal/core/parser.go` for parsing hosts files, including:
  - Support for standard entries (IPv4, IPv6, multiple aliases, inline comments)
  - Handling of comments and disabled entries
  - Error recovery for malformed lines with warnings
  - Intelligent formatting with adaptive spacing and column alignment
  - Backup and atomic write operations for file safety

test(parser): Add comprehensive tests for hosts file parsing

- Created `tests/parser_test.go` with 54 test cases covering:
  - Standard entries and comments
  - Malformed lines and whitespace variations
  - Round-trip parsing to ensure format preservation
  - Backup functionality for hosts files

docs(progress): Update project progress and next steps

- Mark Phase 1 as complete and outline tasks for Phase 2 (TUI implementation)
- Highlight completed features and testing coverage

memory-bank/progress.md

@@ -22,22 +22,35 @@
 - **Test suite**: ✅ Comprehensive tests (44 test cases, 100% passing)
 - **Demo application**: ✅ Working `cmd/hosts/main.go` demonstrating functionality
 
+### ✅ Phase 1: Core Functionality (COMPLETED)
+- **Hosts file parser**: ✅ Complete `internal/core/parser.go` implementation
+- **Intelligent formatting**: ✅ Adaptive spacing and column alignment with GCD-based detection
+- **File operations**: ✅ Safe backup and atomic write operations
+- **Test coverage**: ✅ 54 comprehensive tests (100% passing)
+- **Demo application**: ✅ Full working demonstration with real-world examples
+- **Parser capabilities**:
+  - ✅ **Standard entries**: IPv4, IPv6, multiple aliases, inline comments
+  - ✅ **Comment handling**: Disabled entries vs standalone comments with perfect classification
+  - ✅ **Error recovery**: Malformed line handling with non-fatal warnings
+  - ✅ **Format preservation**: Round-trip parsing maintains style while improving alignment
+  - ✅ **Style detection**: GCD-based tab/space analysis with intelligent column widths
+  - ✅ **Search functionality**: Find entries by hostname or alias with O(1) performance
+- **Safety features**:
+  - ✅ **Backup system**: Timestamped backups in `~/.config/hosts-go/` directory
+  - ✅ **Atomic operations**: Temporary files with rollback capability prevent corruption
+  - ✅ **Validation layers**: Comprehensive IP and hostname validation with clear messages
+  - ✅ **Warning system**: Non-fatal issues reported gracefully without stopping parsing
+  - ✅ **Format intelligence**: Automatic detection and preservation of original formatting style
+
 ## What's Left to Build
 
-### 🚧 Core Functionality (Phase 1 - Current Priority)
-- [ ] **Hosts file parser**: Read and parse `/etc/hosts` file format
-  - [ ] Parse IP addresses, hostnames, comments
-  - [ ] Handle disabled entries (commented out)
-  - [ ] Preserve original formatting and comments
-- [ ] **File operations**: Read hosts file with error handling
-- [ ] **Round-trip parsing**: Parse → modify → write back with format preservation
-
-### 🎨 Basic TUI (Phase 2)  
+### 🎨 Basic TUI (Phase 2 - Current Priority)  
 - [ ] **Main Bubble Tea model**: Core application state and structure
 - [ ] **Two-pane layout**: Left list + right detail view
 - [ ] **Entry list display**: Show active status, IP, hostname columns
 - [ ] **Entry selection**: Navigate and select entries with keyboard
 - [ ] **View mode**: Safe browsing without modification capability
+- [ ] **Integration**: Connect TUI with existing parser functionality
 
 ### 🔧 Edit Functionality (Phase 3)
 - [ ] **Edit mode transition**: Explicit mode switching with visual indicators
@@ -54,18 +67,18 @@
 - [ ] **Search/filter**: Find entries quickly in large files
 
 ### 🧪 Testing & Quality (Ongoing)
-- [ ] **Parser tests**: Round-trip parsing, edge cases, malformed files
-- [ ] **Model tests**: Data validation, entry manipulation
 - [ ] **TUI tests**: User interactions, state transitions
-- [ ] **Integration tests**: Complete workflows, file operations
+- [ ] **Integration tests**: Complete TUI workflows with file operations
 - [ ] **Permission tests**: sudo scenarios, graceful degradation
+- [ ] **End-to-end tests**: Full application workflows
 
 ## Current Status
 
-### Project Phase: **Foundation Complete → Core Functionality**
-- **Completion**: ~25% (foundation and core models complete)
-- **Active work**: Ready to implement hosts file parser (Phase 1)
-- **Blockers**: None - solid foundation established
+### Project Phase: **Phase 1 Complete → Phase 2 (TUI Implementation)**
+- **Completion**: ~65% (foundation and complete core parser functionality implemented)
+- **Active work**: Ready to implement Bubble Tea TUI with two-pane layout (Phase 2)
+- **Blockers**: None - comprehensive parser foundation with 54 tests completed
+- **Parser status**: Production-ready with all safety features implemented
 
 ### Development Readiness
 - ✅ **Architecture designed**: Clear technical approach documented
@@ -74,12 +87,14 @@
 - ✅ **Testing strategy**: TDD approach implemented and proven
 - ✅ **Project scaffolding**: Complete Go module with all dependencies
 - ✅ **Development environment**: Fully functional with comprehensive tests
+- ✅ **Parser foundation**: Robust, tested, and production-ready
 
 ### Risk Assessment
 - **Low risk**: Well-established technology stack (Go + Bubble Tea)
+- **Low risk**: Core parsing functionality (thoroughly tested and working)
+- **Medium risk**: TUI complexity with two-pane layout
 - **Medium risk**: Permission handling complexity (sudo integration)
-- **Low risk**: File format parsing (well-defined `/etc/hosts` format)
-- **Medium risk**: TUI responsiveness with large files
+- **Low risk**: TUI responsiveness (parser handles large files efficiently)
 
 ## Known Issues
 
@@ -142,19 +157,44 @@
 
 ## Next Immediate Actions
 
-### ✅ COMPLETED Foundation Tasks
+### ✅ COMPLETED Phase 1 Tasks
 1. ✅ **Initialize Go project** (`go mod init hosts-go`)
 2. ✅ **Add core dependencies** (Bubble Tea, Bubbles, Lip Gloss, testify)
 3. ✅ **Create directory structure** according to projectbrief.md
-4. ✅ **Create core data models** with comprehensive validation
-5. ✅ **Implement test suite** (44 tests, 100% passing)
-6. ✅ **Create demo application** proving foundation works
+4. ✅ **Create core data models** with comprehensive validation (`internal/core/models.go`)
+5. ✅ **Implement foundation test suite** (44 model tests, 100% passing)
+6. ✅ **Create demo application** proving foundation works (`cmd/hosts/main.go`)
+7. ✅ **Write comprehensive parser tests** (54 total tests covering all scenarios)
+8. ✅ **Implement hosts file parser** (`internal/core/parser.go` - complete implementation)
+9. ✅ **Add intelligent formatting system** with GCD-based spacing detection
+10. ✅ **Implement safe file operations** with backup and atomic writes
+11. ✅ **Handle edge cases** (malformed entries, various formats, error recovery)
+12. ✅ **Test round-trip parsing** (parse → format → parse consistency verified)
+13. ✅ **Update demo application** showcasing all parser functionality with realistic examples
+14. ✅ **Implement search functionality** (FindEntry method for hostname/alias lookup)
+15. ✅ **Add format style detection** (automatic tab vs space detection with column widths)
+16. ✅ **Create backup system** (timestamped backups in `~/.config/hosts-go/`)
+17. ✅ **Validate all parser features** (IPv4, IPv6, aliases, comments, disabled entries)
+18. ✅ **Test warning system** (malformed lines handled gracefully)
+19. ✅ **Verify atomic operations** (temp files with rollback for safe writes)
+20. ✅ **Complete parser documentation** (comprehensive demo showing all capabilities)
 
-### 🚧 NEXT Phase 1 Actions (Hosts File Parser)
-1. **Write parser tests** for `/etc/hosts` file format parsing
-2. **Implement hosts file reader** (`internal/core/parser.go`)
-3. **Add line-by-line parsing logic** with comment preservation
-4. **Test round-trip parsing** (read → parse → write)
-5. **Handle edge cases** (malformed entries, various formats)
+### 🚧 NEXT Phase 2 Actions (TUI Implementation)
+1. **Design TUI architecture** following Bubble Tea MVU pattern
+2. **Create main application model** with state management
+3. **Implement two-pane layout** (entry list + detail view)
+4. **Add navigation controls** (keyboard-driven interaction)
+5. **Integrate parser functionality** with TUI display
+6. **Implement view mode** (safe browsing without modifications)
 
-The foundation is now solid and ready for implementing the core parsing functionality.
+**Phase 1 is fully complete with a production-ready parser foundation.**
+
+### Parser Achievement Summary
+- **54 comprehensive tests** covering all hosts file variations and edge cases
+- **Real-world validation** with complex hosts file examples including IPv4, IPv6, aliases, comments
+- **Intelligent formatting** that preserves user style while improving alignment
+- **Complete safety system** with backups, atomic writes, and graceful error handling
+- **Search and management** capabilities for finding and manipulating entries
+- **Demo application** showcasing all functionality with realistic examples
+
+The foundation is robust, tested, and ready for TUI implementation in Phase 2.