feat(search+docs): trigram fuzzy search, brand/country filters, developer docs

Search:
- migration 0009: trigram GIN index on brand.name + btree on country_of_origin
- SearchProducts: typo-tolerant word_similarity matching (>=0.42) on top of
  ILIKE substring + barcode; new brand/country filters; rank by
  similarity * (0.5 + quality_score). Response gains country_of_origin,
  quality_score and per-result relevance score.
- public search UI: brand/country filter inputs; show country in results

Docs:
- serve embedded OpenAPI 3 spec at GET /api/v1/openapi.json (not rate limited)
- ApiDocs page: auth + rate-limit section, updated search params/response
- docs/api.md developer guide

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

public-frontend/src/types.ts

@@ -4,6 +4,9 @@ export interface ProductSummary {
   name: string;
   brand: string | null;
   category_path: string | null;
+  country_of_origin?: string | null;
+  quality_score?: number;
+  score?: number | null;
 }
 
 export interface Barcode {