feat(opencode): sync all providers to live config on directory change

Add additive mode support for OpenCode in sync_current_to_live:
- Add AppType::is_additive_mode() to distinguish switch vs additive mode
- Add AppType::all() iterator to avoid hardcoding app lists
- Add sync_all_providers_to_live() for additive mode apps
- Refactor sync_current_to_live to handle both modes

Frontend changes (directory settings):
- Track opencodeDirChanged in useDirectorySettings
- Trigger syncCurrentProvidersLiveSafe when OpenCode dir changes
- Add i18n strings for OpenCode directory settings

src/hooks/useSettingsForm.ts

@@ -87,6 +87,8 @@ export function useSettingsForm(): UseSettingsFormResult {
       skipClaudeOnboarding: data.skipClaudeOnboarding ?? false,
       claudeConfigDir: sanitizeDir(data.claudeConfigDir),
       codexConfigDir: sanitizeDir(data.codexConfigDir),
+      geminiConfigDir: sanitizeDir(data.geminiConfigDir),
+      opencodeConfigDir: sanitizeDir(data.opencodeConfigDir),
       language: normalizedLanguage,
     };
 
@@ -143,6 +145,8 @@ export function useSettingsForm(): UseSettingsFormResult {
         skipClaudeOnboarding: serverData.skipClaudeOnboarding ?? false,
         claudeConfigDir: sanitizeDir(serverData.claudeConfigDir),
         codexConfigDir: sanitizeDir(serverData.codexConfigDir),
+        geminiConfigDir: sanitizeDir(serverData.geminiConfigDir),
+        opencodeConfigDir: sanitizeDir(serverData.opencodeConfigDir),
         language: normalizedLanguage,
       };