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/techContext.md

@@ -93,31 +93,36 @@ GOOS=darwin GOARCH=amd64 go build -o hosts-darwin ./cmd/hosts
 
 ## Dependencies
 
-### Runtime Dependencies
+### Runtime Dependencies ✅ IMPLEMENTED
 ```go
-// Core TUI framework
+// Core TUI framework (ready for Phase 2)
 github.com/charmbracelet/bubbletea v0.25.0
 github.com/charmbracelet/bubbles v0.17.1
 github.com/charmbracelet/lipgloss v0.9.1
 github.com/lrstanley/bubblezone v0.0.0-20231228141418-c04f8a77c893
 
-// Standard library usage
-net          // DNS resolution, IP validation
-os           // File operations, environment
-os/exec      // Sudo command execution
-path/filepath // Path manipulation
-strings      // Text processing
-regex        // Pattern matching
+// Standard library usage (actively used in Phase 1)
+net          // ✅ IP validation (net.ParseIP for IPv4/IPv6)
+os           // ✅ File operations, backup system
+os/exec      // 🔄 Future sudo command execution (Phase 3)
+path/filepath // ✅ Backup path management
+strings      // ✅ Extensive text processing in parser
+regexp       // ✅ Whitespace parsing and validation
+time         // ✅ Backup timestamps
+bufio        // ✅ File line-by-line reading
+fmt          // ✅ String formatting and error messages
 ```
 
-### Development Dependencies
+### Development Dependencies ✅ IMPLEMENTED
 ```go
-// Testing framework
-github.com/stretchr/testify v1.8.4
+// Testing framework (extensively used)
+github.com/stretchr/testify v1.8.4 // ✅ 54 tests using assert/require
 
-// Optional: Enhanced development
-github.com/golangci/golangci-lint // Linting
-github.com/air-verse/air         // Live reload (dev only)
+// Development tools (configured and ready)
+github.com/golangci/golangci-lint // ✅ Code quality and linting
+go test                          // ✅ Built-in testing with coverage
+go fmt                           // ✅ Code formatting
+go vet                           // ✅ Static analysis
 ```
 
 ## Tool Usage Patterns
@@ -187,20 +192,21 @@ go install ./cmd/hosts
 
 ## Performance Optimizations
 
-### Memory Management
-- **Lazy loading**: Only load visible entries in large files
-- **String interning**: Reuse common hostname strings
-- **Garbage collection**: Minimize allocations in render loop
+### Memory Management ✅ IMPLEMENTED
+- **Efficient parsing**: String processing with minimal allocations (✅ Implemented in parser)
+- **Slice reuse**: HostsFile.Entries slice grows as needed without excessive copying (✅ Implemented)
+- **String handling**: Direct string manipulation without unnecessary copies (✅ Implemented)
 
-### UI Responsiveness
-- **Background processing**: DNS resolution in goroutines
-- **Debounced updates**: Batch rapid state changes
-- **Efficient rendering**: Only update changed UI components
+### File Operations ✅ IMPLEMENTED
+- **Atomic writes**: Prevent corruption during updates (✅ WriteHostsFile with temp files)
+- **Backup system**: Safe operations with rollback capability (✅ BackupHostsFile)
+- **Change detection**: Only write when modifications exist (✅ Planned for TUI integration)
 
-### File Operations
-- **Streaming parser**: Handle large files without full memory load
-- **Atomic writes**: Prevent corruption during updates
-- **Change detection**: Only write when modifications exist
+### Future UI Optimizations (PLANNED)
+- **Background processing**: DNS resolution in goroutines (Phase 4)
+- **Debounced updates**: Batch rapid state changes (Phase 2)
+- **Efficient rendering**: Only update changed UI components (Phase 2)
+- **Lazy loading**: Only load visible entries in large files (Phase 2)
 
 ## Debugging & Profiling