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/config/src/index.ts

@@ -36,6 +36,10 @@ export const CONTENT_ROOT =
 
 export const DATABASE_URL = process.env.DATABASE_URL ?? "";
 
+export const EMBED_BASE_URL = process.env.EMBED_BASE_URL ?? "";
+export const EMBED_API_KEY = process.env.EMBED_API_KEY ?? "";
+export const EMBED_MODEL = process.env.EMBED_MODEL ?? "";
+
 if (!DATABASE_URL) {
   // Fail fast with an explicit message instead of a cryptic driver error.
   throw new Error(