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/db/drizzle/0001_document_chunks.sql

@@ -0,0 +1,13 @@
+CREATE TABLE "document_chunks" (
+	"id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+	"document_id" text NOT NULL,
+	"slug" text NOT NULL,
+	"chunk_index" integer NOT NULL,
+	"content" text NOT NULL,
+	"embedding" real[],
+	"created_at" timestamp with time zone DEFAULT now() NOT NULL
+);
+--> statement-breakpoint
+CREATE INDEX "document_chunks_slug_idx" ON "document_chunks" USING btree ("slug");
+--> statement-breakpoint
+ALTER TABLE "document_chunks" ADD CONSTRAINT "document_chunks_document_id_documents_id_fk" FOREIGN KEY ("document_id") REFERENCES "public"."documents"("id") ON DELETE cascade;