feat(settings): add auto-launch on system startup feature

Implement auto-launch functionality with proper state synchronization
and error handling across Windows, macOS, and Linux platforms.

Key changes:
- Add auto_launch module using auto-launch crate 0.5
- Define typed errors (AutoLaunchPathError, AutoLaunchEnableError, etc.)
- Sync system state with settings.json on app startup
- Only call system API when auto-launch state actually changes
- Add UI toggle in Window Settings panel
- Add i18n support for auto-launch settings (en/zh)

Implementation details:
- Settings file (settings.json) is the single source of truth
- On startup, system state is synced to match settings.json
- Error handling uses Rust type system with proper error propagation
- Frontend optimized to avoid unnecessary system API calls

Platform support:
- Windows: HKEY_CURRENT_USER registry modification
- macOS: AppleScript-based launch item (configurable to Launch Agent)
- Linux: XDG autostart desktop file

src/hooks/useSettingsForm.ts

@@ -82,6 +82,7 @@ export function useSettingsForm(): UseSettingsFormResult {
       minimizeToTrayOnClose: data.minimizeToTrayOnClose ?? true,
       enableClaudePluginIntegration:
         data.enableClaudePluginIntegration ?? false,
+      launchOnStartup: data.launchOnStartup ?? false,
       claudeConfigDir: sanitizeDir(data.claudeConfigDir),
       codexConfigDir: sanitizeDir(data.codexConfigDir),
       language: normalizedLanguage,
@@ -101,6 +102,7 @@ export function useSettingsForm(): UseSettingsFormResult {
             showInTray: true,
             minimizeToTrayOnClose: true,
             enableClaudePluginIntegration: false,
+            launchOnStartup: false,
             language: readPersistedLanguage(),
           } as SettingsFormState);
 
@@ -135,6 +137,7 @@ export function useSettingsForm(): UseSettingsFormResult {
         minimizeToTrayOnClose: serverData.minimizeToTrayOnClose ?? true,
         enableClaudePluginIntegration:
           serverData.enableClaudePluginIntegration ?? false,
+        launchOnStartup: serverData.launchOnStartup ?? false,
         claudeConfigDir: sanitizeDir(serverData.claudeConfigDir),
         codexConfigDir: sanitizeDir(serverData.codexConfigDir),
         language: normalizedLanguage,