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

apps/api/src/index.ts

@@ -0,0 +1,26 @@
+import { serve } from "@hono/node-server";
+import { Hono } from "hono";
+import { fetchRequestHandler } from "@trpc/server/adapters/fetch";
+import { db } from "@mcpedia/db";
+import { appRouter } from "./router";
+import type { Context } from "./trpc";
+
+const app = new Hono();
+
+// Health check.
+app.get("/health", (c) => c.json({ ok: true }));
+
+// Mount tRPC at /trpc/*. The fetch adapter is the canonical Bun/Hono adapter.
+app.all("/trpc/*", (c) =>
+  fetchRequestHandler({
+    endpoint: "/trpc",
+    req: c.req.raw,
+    router: appRouter,
+    createContext: (): Context => ({ db }),
+  }),
+);
+
+const port = Number(process.env.API_PORT ?? 4020);
+serve({ fetch: app.fetch, port }, (info) => {
+  console.log(`MCPedia API listening on http://localhost:${info.port}`);
+});