feat(knowledge): add tag management API (KNOW-003)

- Add Tag DTOs (CreateTagDto, UpdateTagDto) with validation
- Implement TagsService with CRUD operations
- Add TagsController with authenticated endpoints
- Support automatic slug generation from tag names
- Add workspace isolation for tags
- Include entry count in tag responses
- Add findOrCreateTags method for entry creation/update
- Implement comprehensive test coverage (29 tests passing)

Endpoints:
- GET /api/knowledge/tags - List workspace tags
- POST /api/knowledge/tags - Create tag
- GET /api/knowledge/tags/:slug - Get tag by slug
- PUT /api/knowledge/tags/:slug - Update tag
- DELETE /api/knowledge/tags/:slug - Delete tag
- GET /api/knowledge/tags/:slug/entries - List entries with tag

Related: KNOW-003

apps/api/package.json

@@ -32,11 +32,14 @@
     "@nestjs/core": "^11.1.12",
     "@nestjs/platform-express": "^11.1.12",
     "@prisma/client": "^6.19.2",
+    "@types/marked": "^6.0.0",
     "better-auth": "^1.4.17",
     "class-transformer": "^0.5.1",
     "class-validator": "^0.14.3",
+    "marked": "^17.0.1",
     "reflect-metadata": "^0.2.2",
-    "rxjs": "^7.8.1"
+    "rxjs": "^7.8.1",
+    "slugify": "^1.6.6"
   },
   "devDependencies": {
     "@better-auth/cli": "^1.4.17",