feat(#66): implement tag filtering in search API endpoint

Add support for filtering search results by tags in the main search endpoint.

Changes:
- Add tags parameter to SearchQueryDto (comma-separated tag slugs)
- Implement tag filtering in SearchService.search() method
- Update SQL query to join with knowledge_entry_tags when tags provided
- Entries must have ALL specified tags (AND logic)
- Add tests for tag filtering (2 controller tests, 2 service tests)
- Update endpoint documentation
- Fix non-null assertion linting error

The search endpoint now supports:
- Full-text search with ranking (ts_rank)
- Snippet generation with highlighting (ts_headline)
- Status filtering
- Tag filtering (new)
- Pagination

Example: GET /api/knowledge/search?q=api&tags=documentation,tutorial

All tests pass (25 total), type checking passes, linting passes.

Fixes #66

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/orchestrator/src/spawner/spawner.module.ts

@@ -1,4 +1,8 @@
 import { Module } from "@nestjs/common";
+import { AgentSpawnerService } from "./agent-spawner.service";
 
-@Module({})
+@Module({
+  providers: [AgentSpawnerService],
+  exports: [AgentSpawnerService],
+})
 export class SpawnerModule {}