fix: add missing /api/admin/learning/knowledge-bases endpoint

Dashboard filter dropdown calls this to populate KB selector.
Returns knowledge bases that have reading event data with real titles.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/modules/admin-learning/admin-learning.controller.ts

@@ -16,6 +16,10 @@ export class AdminLearningController {
     @Query('endDate') endDate?: string,
   ) { return this.service.getDashboard({ knowledgeBaseId, startDate, endDate }); }
 
+  // ── Knowledge Bases ──
+  @Get('knowledge-bases')
+  async getKnowledgeBases() { return this.service.getKnowledgeBases(); }
+
   // ── ReadingEvents ──
   @Get('reading-events')
   async getReadingEvents(@Query() query: EventFilterQuery) { return this.service.getReadingEvents(query); }

src/modules/admin-learning/admin-learning.service.ts

@@ -9,6 +9,28 @@ export class AdminLearningService {
     private readonly snapshotBuilder: SnapshotBuilderService,
   ) {}
 
+  // ══ Knowledge Bases (for filter dropdown) ══
+
+  async getKnowledgeBases() {
+    // Return knowledge bases that appear in reading_events, with real names from KB table
+    const ids = await this.prisma.readingEvent.findMany({
+      where: { knowledgeBaseId: { not: null } },
+      select: { knowledgeBaseId: true },
+      distinct: ['knowledgeBaseId'],
+      take: 200,
+    });
+    const kbIds = [...new Set(ids.map(r => r.knowledgeBaseId!).filter(Boolean))];
+
+    if (kbIds.length === 0) return [];
+
+    const kbs = await this.prisma.knowledgeBase.findMany({
+      where: { id: { in: kbIds } },
+      select: { id: true, title: true },
+      take: 200,
+    });
+    return kbs.map(kb => ({ id: kb.id, name: kb.title }));
+  }
+
   // ══ Dashboard ══
 
   async getDashboard(filters?: { knowledgeBaseId?: string; startDate?: string; endDate?: string }) {