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-tauri/src/app_config.rs

@@ -282,6 +282,25 @@ impl AppType {
             AppType::OpenCode => "opencode",
         }
     }
+
+    /// Check if this app uses additive mode
+    ///
+    /// - Switch mode (false): Only the current provider is written to live config (Claude, Codex, Gemini)
+    /// - Additive mode (true): All providers are written to live config (OpenCode)
+    pub fn is_additive_mode(&self) -> bool {
+        matches!(self, AppType::OpenCode)
+    }
+
+    /// Return an iterator over all app types
+    pub fn all() -> impl Iterator<Item = AppType> {
+        [
+            AppType::Claude,
+            AppType::Codex,
+            AppType::Gemini,
+            AppType::OpenCode,
+        ]
+        .into_iter()
+    }
 }
 
 impl FromStr for AppType {