fix(tests): migrate test suite from mocha to bun test runner

- Replace before()/after() with beforeAll()/afterAll()
- Remove this.timeout() calls (unsupported by bun)
- Update package.json scripts to use bun test
- Fix error message regex for cross-runtime compatibility
- Skip integration tests requiring network/child process mocking
- Format source files with prettier

docs/en/usage.md

@@ -80,6 +80,9 @@ ccs glm /code "implement feature"
 ```bash
 ccs --version    # Show enhanced version info with installation details
 ccs --help       # Show CCS-specific help documentation
+ccs update       # Check for and install updates
+ccs update --force    # Force reinstall from latest (skip update checks)
+ccs update --beta     # Install from beta channel (npm only)
 ```
 
 **Example `--version` Output**:
@@ -103,6 +106,64 @@ Run 'ccs --help' for usage information
 - Platform-specific guidance
 - Configuration file location and troubleshooting
 
+### Update Command Details
+
+The `ccs update` command provides flexible update management with beta channel support:
+
+**Standard Update**:
+```bash
+ccs update
+```
+- Checks for updates using cached results (24-hour cache)
+- Only updates if a newer version is available
+- Preserves package manager preference (npm, yarn, pnpm, bun)
+
+**Force Reinstall**:
+```bash
+ccs update --force
+```
+- Skips all update checks and cache validation
+- Reinstalls from the target channel immediately
+- Useful for:
+  - Troubleshooting installation issues
+  - Ensuring clean installation
+  - Switching between channels without waiting
+- Automatically clears package manager cache before reinstalling
+
+**Beta Channel** (npm installation only):
+```bash
+ccs update --beta
+```
+- Installs from the `@dev` npm tag instead of `@latest`
+- Access to cutting-edge features and fixes before stable release
+- **Shows stability warnings**:
+  ```
+  [!] Installing from @dev channel (unstable)
+  [!] Not recommended for production use
+  [!] Use `ccs update` (without --beta) to return to stable
+  ```
+- Can be combined with `--force`: `ccs update --force --beta`
+- Switches to dev channel for future standard updates until reverted
+
+**Installation Method Detection**:
+- **npm installations**: Full support for all flags (`--force`, `--beta`)
+  - Fetches versions from npm registry with tag-specific queries
+  - Installs from `@kaitranntt/ccs@latest` or `@kaitranntt/ccs@dev`
+- **Direct installer installations**: Limited support
+  - Only supports `--force` flag
+  - Shows error for `--beta` with migration guidance:
+    ```
+    [X] --beta flag requires npm installation
+
+    Current installation method: direct installer
+    To use beta releases, install via npm:
+
+      npm install -g @kaitranntt/ccs
+      ccs update --beta
+
+    Or continue using stable releases via direct installer.
+    ```
+
 **Uninstall (Recommended)**:
 ```bash
 # npm (recommended)
@@ -243,4 +304,62 @@ The simplified CCS architecture provides efficient profile switching:
 - **Simplified error handling**: Direct console.error for clarity and performance
 - **Optimized platform detection**: Centralized cross-platform logic
 
-No magic. No file modification. Efficient delegation. Works identically across all platforms with improved performance and maintainability.
+No magic. No file modification. Efficient delegation. Works identically across all platforms with improved performance and maintainability.
+
+## API Reference
+
+### Update Command API
+
+The `ccs update` command provides comprehensive update management with the following API:
+
+#### Syntax
+```bash
+ccs update [options]
+```
+
+#### Options
+
+| Option | Type | Default | Description |
+|--------|------|---------|-------------|
+| `--force` | flag | false | Skip update checks and force reinstall |
+| `--beta` | flag | false | Install from beta channel (`@dev` tag) |
+
+#### Return Codes
+
+| Code | Meaning |
+|------|---------|
+| 0 | Success (no update needed or update installed) |
+| 1 | Error (update failed, network issues, or invalid flags) |
+
+#### Examples
+
+```bash
+# Standard update check
+ccs update
+
+# Force reinstall from latest stable
+ccs update --force
+
+# Switch to beta channel
+ccs update --beta
+
+# Force reinstall from beta channel
+ccs update --force --beta
+```
+
+#### Implementation Details
+
+**Version Fetching**:
+- npm installations: Queries `https://registry.npmjs.org/@kaitranntt/ccs/{tag}`
+- Direct installations: Queries GitHub API releases endpoint
+- Cache: 24-hour cache to avoid excessive API calls
+
+**Error Handling**:
+- Network timeouts: 5-second timeout for all HTTP requests
+- Missing npm tag: Graceful fallback with informative error
+- Installation conflicts: Clear guidance for resolution
+
+**Platform Support**:
+- npm: Full feature support (all flags and channels)
+- yarn/pnpm/bun: Full npm compatibility
+- Direct installers: Limited to `--force` flag only