fix(plugins): wire up translation loading to i18n service (CRITICAL)

Fixes the critical issue where translations were loaded but never
passed to PluginI18nService, making the i18n system non-functional.

Changes:
- Inject PluginI18nService in PluginService
- Load translations into i18n service in 3 locations:
  - _loadPluginLazy() for lazy-loaded plugins
  - _loadPlugin() for file-based plugins
  - _loadUploadedPlugin() for cached plugins
- Improve LANGUAGE_CHANGE hook type guard
  - Use explicit LanguageCode type predicate
  - Remove non-null assertion (no longer needed)

This makes api.translate() functional for all plugin loading paths.

src/app/plugins/plugin-hooks.effects.ts

@@ -45,6 +45,7 @@ import {
 } from '../features/work-context/store/work-context-meta.actions';
 import { LOCAL_ACTIONS } from '../util/local-actions.token';
 import { PlannerActions } from '../features/planner/store/planner.actions';
+import { LanguageCode } from '../core/locale.constants';
 
 @Injectable()
 export class PluginHooksEffects {
@@ -210,11 +211,11 @@ export class PluginHooksEffects {
         filter((action) => action.sectionKey === 'localization'),
         withLatestFrom(this.store.pipe(select(selectLocalizationConfig))),
         map(([_, localizationConfig]) => localizationConfig.lng),
-        filter((lng) => !!lng),
+        filter((lng): lng is LanguageCode => typeof lng === 'string' && lng.length > 0),
         distinctUntilChanged(),
         tap((newLanguage) => {
           // Update plugin i18n service with new language
-          this.pluginI18nService.setCurrentLanguage(newLanguage!);
+          this.pluginI18nService.setCurrentLanguage(newLanguage);
 
           // Dispatch hook to notify plugins
           this.pluginService.dispatchHook(PluginHooks.LANGUAGE_CHANGE, {

src/app/plugins/plugin.service.ts

@@ -31,6 +31,7 @@ import { validatePluginManifest } from './util/validate-manifest.util';
 import { TranslateService } from '@ngx-translate/core';
 import { T } from '../t.const';
 import { PluginLog } from '../core/log';
+import { PluginI18nService } from './plugin-i18n.service';
 
 @Injectable({
   providedIn: 'root',
@@ -48,6 +49,7 @@ export class PluginService implements OnDestroy {
   private readonly _cleanupService = inject(PluginCleanupService);
   private readonly _pluginLoader = inject(PluginLoaderService);
   private readonly _translateService = inject(TranslateService);
+  private readonly _pluginI18nService = inject(PluginI18nService);
 
   private _isInitialized = false;
   private _loadedPlugins: PluginInstance[] = [];
@@ -373,13 +375,21 @@ export class PluginService implements OnDestroy {
   private async _loadPluginLazy(state: PluginState): Promise<PluginInstance> {
     // Load the plugin code and assets
     const assets = await this._pluginLoader.loadPluginAssets(state.path);
-    const { code: pluginCode, indexHtml } = assets;
+    const { code: pluginCode, indexHtml, translations } = assets;
 
     // Store assets
     if (indexHtml) {
       this._pluginIndexHtml.set(state.manifest.id, indexHtml);
     }
 
+    // Load translations into i18n service
+    if (translations && Object.keys(translations).length > 0) {
+      this._pluginI18nService.loadPluginTranslationsFromContent(
+        state.manifest.id,
+        translations,
+      );
+    }
+
     // Create base config
     const baseCfg = this._getBaseCfg();
 
@@ -454,7 +464,7 @@ export class PluginService implements OnDestroy {
     try {
       // Use the loader service for lazy loading
       const assets = await this._pluginLoader.loadPluginAssets(pluginPath);
-      const { manifest, code: pluginCode, indexHtml, icon } = assets;
+      const { manifest, code: pluginCode, indexHtml, icon, translations } = assets;
 
       // Store assets if loaded
       if (indexHtml) {
@@ -466,6 +476,14 @@ export class PluginService implements OnDestroy {
         this._pluginIconsSignal.set(new Map(this._pluginIcons));
       }
 
+      // Load translations into i18n service
+      if (translations && Object.keys(translations).length > 0) {
+        this._pluginI18nService.loadPluginTranslationsFromContent(
+          manifest.id,
+          translations,
+        );
+      }
+
       // Check if plugin should be loaded based on persisted enabled state
       const isPluginEnabled = await this._pluginMetaPersistenceService.isPluginEnabled(
         manifest.id,
@@ -1210,7 +1228,7 @@ export class PluginService implements OnDestroy {
     try {
       // Use the loader service for uploaded plugins
       const assets = await this._pluginLoader.loadUploadedPluginAssets(pluginId);
-      const { manifest, code: pluginCode, indexHtml, icon } = assets;
+      const { manifest, code: pluginCode, indexHtml, icon, translations } = assets;
 
       // Store assets if loaded
       if (indexHtml) {
@@ -1222,6 +1240,14 @@ export class PluginService implements OnDestroy {
         this._pluginIconsSignal.set(new Map(this._pluginIcons));
       }
 
+      // Load translations into i18n service
+      if (translations && Object.keys(translations).length > 0) {
+        this._pluginI18nService.loadPluginTranslationsFromContent(
+          manifest.id,
+          translations,
+        );
+      }
+
       // Validate manifest
       const manifestValidation = validatePluginManifest(manifest);
       if (!manifestValidation.isValid) {