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/vitest.config.ts

@@ -0,0 +1,29 @@
+import { defineConfig } from "vitest/config";
+
+export default defineConfig({
+  test: {
+    globals: true,
+    environment: "node",
+    exclude: ["**/node_modules/**", "**/dist/**", "**/tests/integration/**"],
+    include: ["src/**/*.spec.ts", "src/**/*.test.ts"],
+    coverage: {
+      provider: "v8",
+      reporter: ["text", "json", "html"],
+      exclude: [
+        "**/node_modules/**",
+        "**/dist/**",
+        "**/*.spec.ts",
+        "**/*.test.ts",
+        "**/types/**",
+        "**/*.module.ts",
+        "**/main.ts",
+      ],
+      thresholds: {
+        lines: 85,
+        functions: 85,
+        branches: 85,
+        statements: 85,
+      },
+    },
+  },
+});