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/i18n/locales/en.json

@@ -327,9 +327,12 @@
     "codexConfigDirDescription": "Override Codex configuration directory.",
     "geminiConfigDir": "Gemini Configuration Directory",
     "geminiConfigDirDescription": "Override Gemini configuration directory (.env).",
+    "opencodeConfigDir": "OpenCode Configuration Directory",
+    "opencodeConfigDirDescription": "Override OpenCode configuration directory (opencode.json).",
     "browsePlaceholderClaude": "e.g., /home/<your-username>/.claude",
     "browsePlaceholderCodex": "e.g., /home/<your-username>/.codex",
     "browsePlaceholderGemini": "e.g., /home/<your-username>/.gemini",
+    "browsePlaceholderOpencode": "e.g., /home/<your-username>/.config/opencode",
     "browseDirectory": "Browse Directory",
     "resetDefault": "Reset to default directory (takes effect after saving)",
     "checkForUpdates": "Check for Updates",

src/i18n/locales/ja.json

@@ -327,9 +327,12 @@
     "codexConfigDirDescription": "Codex の設定ディレクトリを上書きします。",
     "geminiConfigDir": "Gemini 設定ディレクトリ",
     "geminiConfigDirDescription": "Gemini の設定ディレクトリ（.env）を上書きします。",
+    "opencodeConfigDir": "OpenCode 設定ディレクトリ",
+    "opencodeConfigDirDescription": "OpenCode の設定ディレクトリ（opencode.json）を上書きします。",
     "browsePlaceholderClaude": "例: /home/<your-username>/.claude",
     "browsePlaceholderCodex": "例: /home/<your-username>/.codex",
     "browsePlaceholderGemini": "例: /home/<your-username>/.gemini",
+    "browsePlaceholderOpencode": "例: /home/<your-username>/.config/opencode",
     "browseDirectory": "ディレクトリを選択",
     "resetDefault": "デフォルトに戻す（保存後に反映）",
     "checkForUpdates": "アップデートを確認",

src/i18n/locales/zh.json

@@ -327,9 +327,12 @@
     "codexConfigDirDescription": "覆盖 Codex 配置目录。",
     "geminiConfigDir": "Gemini 配置目录",
     "geminiConfigDirDescription": "覆盖 Gemini 配置目录 (.env)。",
+    "opencodeConfigDir": "OpenCode 配置目录",
+    "opencodeConfigDirDescription": "覆盖 OpenCode 配置目录 (opencode.json)。",
     "browsePlaceholderClaude": "例如：/home/<你的用户名>/.claude",
     "browsePlaceholderCodex": "例如：/home/<你的用户名>/.codex",
     "browsePlaceholderGemini": "例如：/home/<你的用户名>/.gemini",
+    "browsePlaceholderOpencode": "例如：/home/<你的用户名>/.config/opencode",
     "browseDirectory": "浏览目录",
     "resetDefault": "恢复默认目录（需保存后生效）",
     "checkForUpdates": "检查更新",