feat(mcpedia): Phase 2 — semantic + hybrid search, tRPC/Hono API

- @mcpedia/embeddings: OpenRouter provider (9router /v1, encoding_format float),
  chunkText + embedChunks; EMBED_DIM=2048
- document_chunks table (real[] embedding) — pgvector NOT available on shared
  imrnes Postgres, so cosine is computed in-app (KB-scale fine); pgvector deferred
- indexer: chunk + embed + upsert per document
- @mcpedia/search: semanticSearch (cosine) + hybridSearch (FTS+cosine RRF)
- apps/api: Hono + tRPC v11 (6 procedures), serve on :4020
- MCP: semantic_search + hybrid_search tools (6 total)
- web: keyword/hybrid toggle; .env.example + README + PHASES updated

packages/core/package.json

@@ -10,6 +10,7 @@
   "dependencies": {
     "@mcpedia/config": "workspace:*",
     "@mcpedia/db": "workspace:*",
+    "@mcpedia/embeddings": "workspace:*",
     "@mcpedia/parser": "workspace:*",
     "@mcpedia/search": "workspace:*",
     "@mcpedia/types": "workspace:*",