feat: Add powerful CLI for account management (#115)

* feat: Add powerful CLI for account management

- 18 commands for quota monitoring, switching, validation
- Interactive mode with keyboard navigation
- Smart auto-switch based on quotas
- Alias support for quick access
- Token auto-refresh and diagnostics
- Full documentation in cli/README.md"

* fix: Address code review issues - Add SQLite transactions for atomicity\n- Add input validation for import_accounts\n- Add per-account error handling in bulk operations\n- Add graceful error handling in interactive mode\n- Add validation for varint encoding (negative values)\n- Improve user feedback on partial failures

cli/README.md

@@ -0,0 +1,197 @@
+# Antigravity Manager CLI
+
+A powerful command-line interface for managing multiple Google Cloud AI accounts in Antigravity IDE. Supports account switching, quota monitoring, token validation, and more.
+
+## Features
+
+- 📊 **Quota Management**: Real-time quota tracking for Gemini and Claude models
+- 🔄 **Account Switching**: Seamless switching between multiple Google accounts
+- ✅ **Token Validation**: Automatic token refresh and expiry detection
+- 🎯 **Smart Auto-Switch**: Automatically select the best account based on quotas
+- 🏷️ **Aliases**: Create shortcuts for your accounts (e.g., `work`, `personal`)
+- 💾 **Backup/Restore**: Export and import account configurations
+- 🔍 **Database Sync**: View sync status between CLI and IDE
+- 🩺 **Diagnostics**: System health checks and troubleshooting
+- 🎮 **Interactive Mode**: Beautiful keyboard-navigated menus
+
+## Installation
+
+1. **Install Python dependencies:**
+   ```powershell
+   pip install -r requirements.txt
+   ```
+
+2. **(Optional) Add to PATH:**
+   ```powershell
+   .\agm.bat setup-path
+   ```
+   Restart your terminal after this.
+
+## Quick Start
+
+### Interactive Mode (Recommended for Beginners)
+Simply run without arguments to get a menu:
+```powershell
+.\agm.bat
+```
+
+### Command Line (For Power Users)
+
+**List all accounts:**
+```powershell
+agm list
+```
+
+**Switch accounts:**
+```powershell
+agm switch [email protected]
+# or use partial match
+agm switch aleks
+```
+
+**Refresh quotas:**
+```powershell
+agm refresh-all
+# or single account
+agm refresh [email protected]
+```
+
+**Validate tokens:**
+```powershell
+agm validate
+```
+
+**Quick status:**
+```powershell
+agm status
+```
+
+## Advanced Features
+
+### Aliases
+Create shortcuts for frequently used accounts:
+```powershell
+# Set alias
+agm alias work [email protected]
+
+# Use alias
+agm switch work
+agm refresh work
+
+# View all aliases
+agm alias
+
+# Remove alias
+agm unalias work
+```
+
+### Auto-Switch
+Automatically switch to the account with the best quota:
+```powershell
+# Any model with at least 50% quota
+agm auto-switch
+
+# Prefer Claude models
+agm auto-switch --model claude --min-quota 30
+
+# Prefer Gemini models
+agm auto-switch --model gemini --min-quota 60
+```
+
+### Backup & Restore
+```powershell
+# Export accounts
+agm export my_accounts.json
+
+# Import accounts
+agm import-backup my_accounts.json
+```
+
+### Live Monitoring
+Watch quota changes in real-time:
+```powershell
+# Refresh every 10 seconds (default)
+agm watch
+
+# Custom interval
+agm watch --interval 30
+```
+
+### Diagnostics
+Run system health checks:
+```powershell
+agm doctor
+```
+
+## All Commands
+
+| Command | Description |
+|---------|-------------|
+| `agm list` | List all accounts with quota summary |
+| `agm info <email>` | Show detailed quota for specific account |
+| `agm switch <email>` | Switch to an account |
+| `agm status` | Show active account and quotas |
+| `agm refresh <email>` | Refresh quotas for one account |
+| `agm refresh-all` | Refresh quotas for all accounts |
+| `agm validate` | Check and refresh expired tokens |
+| `agm sync` | Show CLI ↔ IDE sync status |
+| `agm remove <email>` | Delete an account from database |
+| `agm alias [name] [email]` | Manage account aliases |
+| `agm unalias <name>` | Remove an alias |
+| `agm export [file]` | Export accounts to JSON |
+| `agm import-backup <file>` | Import accounts from backup |
+| `agm auto-switch` | Switch to best account automatically |
+| `agm watch [--interval N]` | Live quota monitoring |
+| `agm doctor` | Run system diagnostics |
+| `agm setup-path` | Add CLI to Windows PATH |
+
+## How It Works
+
+The CLI interacts directly with the Antigravity Manager's encrypted database:
+
+1. **Database Location**: Auto-discovers the database in `%APPDATA%\AntigravityManager` or IDE installation directory
+2. **Encryption**: Uses Windows DPAPI + AES-256-GCM to decrypt account tokens (same as the IDE)
+3. **Quota API**: Fetches live quota data from Google Cloud AI REST API
+4. **Process Control**: Can start/stop the IDE executable automatically
+
+## Troubleshooting
+
+**"Database not found" error:**
+- Ensure Antigravity Manager has been run at least once
+- Check if accounts exist in the GUI first
+
+**"Failed to decrypt" error:**
+- Run `agm doctor` to diagnose
+- Ensure you're on the same Windows user account
+
+**"Token expired" warnings:**
+- Run `agm validate` to auto-refresh all tokens
+
+**Quota not updating:**
+- Run `agm refresh-all` to force update
+- Check network connection
+
+## Requirements
+
+- Windows 10/11
+- Python 3.8+
+- Antigravity Manager (for database access)
+
+## Development
+
+The CLI is split into two main modules:
+
+- **`core.py`**: Core functionality (database access, API calls, encryption)
+- **`main.py`**: Command definitions and interactive UI
+- **`proto_utils.py`**: Protobuf encoding helpers
+
+## License
+
+Same as parent project.
+
+## Contributing
+
+Pull requests welcome! Please ensure:
+- Code follows existing style
+- All commands have help text
+- No hardcoded paths or credentials