feat: Initialize hosts-go project with foundational structure and core functionality

- Created activeContext.md and productContext.md to outline project goals and current focus.
- Established progress.md to track project milestones and tasks.
- Developed projectbrief.md detailing application overview, requirements, and directory structure.
- Documented systemPatterns.md to describe architecture and design patterns used.
- Compiled techContext.md to specify technologies and development setup.
- Implemented comprehensive unit tests in models_test.go for HostEntry and HostsFile functionalities.

memory-bank/productContext.md

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+# Product Context: hosts-go
+
+## Why This Project Exists
+
+The `/etc/hosts` file is a critical system file that maps hostnames to IP addresses, but managing it manually is cumbersome and error-prone. Users currently face several pain points:
+
+- **Manual editing**: Requires opening `/etc/hosts` in a text editor with sudo privileges
+- **Format preservation**: Easy to accidentally break formatting or lose comments
+- **Entry management**: No easy way to temporarily disable entries without deleting them
+- **DNS resolution**: Manual IP address updates when hostnames change
+- **Organization**: No built-in sorting or reordering capabilities
+
+## Problems It Solves
+
+1. **Safe editing**: Provides a structured interface that validates changes before writing
+2. **Entry activation**: Toggle entries on/off without losing the configuration
+3. **Organization**: Sort and reorder entries intuitively
+4. **DNS integration**: Automatically resolve hostnames to current IP addresses
+5. **Comment preservation**: Maintain documentation alongside entries
+6. **Permission handling**: Only request sudo access when actually editing
+
+## How It Should Work
+
+### Core User Experience
+- **View mode by default**: Browse entries safely without modification risk
+- **Explicit edit mode**: Clear transition to editing with permission request
+- **Two-pane interface**: List view + detail view for efficient navigation
+- **Keyboard-driven**: Fast navigation and actions via keyboard shortcuts
+- **Visual feedback**: Clear indicators for active/inactive entries and changes
+
+### Key Workflows
+
+1. **Browse entries**: Launch app, see all current hosts entries with status
+2. **Quick activation**: Toggle entries on/off with simple keypress
+3. **Edit existing**: Select entry, enter edit mode, modify details
+4. **Add new**: Create new hostname mappings with validation
+5. **DNS resolution**: Update IP addresses automatically from DNS
+6. **Reorder entries**: Drag/move entries to organize logically
+
+## User Experience Goals
+
+### Immediate Value
+- **Zero learning curve**: Intuitive interface familiar to CLI users
+- **Safety first**: Hard to accidentally break the hosts file
+- **Speed**: Faster than manual editing for common tasks
+
+### Long-term Benefits
+- **Organized hosts**: Keep entries structured and documented
+- **Confidence**: Know changes are validated before applied
+- **Efficiency**: Common tasks become single keystrokes
+
+### Target Users
+- **Developers**: Managing local development environments
+- **System administrators**: Bulk hosts file management
+- **Network engineers**: Testing connectivity and DNS overrides
+- **Security professionals**: Blocking/redirecting malicious domains
+
+## Success Metrics
+- Users prefer this tool over manual `/etc/hosts` editing
+- Reduces hosts file corruption incidents
+- Speeds up common host management tasks
+- Provides confidence in making changes