feat(mcpedia): Phase 3 — async indexing (BullMQ), git-sync webhook, revisions, MCP Resources

- packages/queue: ioredis singleton + BullMQ Queue/Worker (prefix mcpedia:
  on shared imrnes Redis :6379); apps/worker runs startWorker()
- @mcpedia/core: indexContentFile/runFullIndex (single indexing entry point
  shared by script/worker/hook) + revision.service (list/get/restore)
- document_revisions table (migration 0002) — snapshots only on body change
- apps/api: POST /hooks/reindex + /hooks/index webhooks; tRPC revisions,
  getRevision, restoreRevision, jobStatus, queueStatus
- apps/mcp: register MCP Resources mcpedia://docs{/,+slug/chunks/revisions}
  ({+slug} RFC6570 reserved expansion for slugs containing /)
- apps/mcp zod pinned to ^4 to match MCP SDK 1.30 compiled types
  (resolves registerTool TS2589/ShapeOutput skew)
- scripts/enqueue.ts one-shot job enqueue helper; indexer refactored to runFullIndex
- PHASES.md/README/.env.example/docs updated

packages/queue/src/client.ts

@@ -0,0 +1,34 @@
+import { REDIS_URL, REDIS_PASSWORD, QUEUE_PREFIX } from "@mcpedia/config";
+import IORedis, { type RedisOptions } from "ioredis";
+
+/**
+ * Shared ioredis connection for BullMQ. BullMQ requires an ioredis instance and
+ * internally duplicates it for blocking commands, so we keep the option objects
+ * explicit (maxRetriesPerRequest: null is REQUIRED for the blocking
+ * connection — a finite retry count causes "Connection in key mode" errors).
+ */
+function buildOptions(): RedisOptions {
+  const opts: RedisOptions = {
+    maxRetriesPerRequest: null,
+    lazyConnect: true,
+    enableOfflineQueue: true,
+  };
+  if (REDIS_PASSWORD) opts.password = REDIS_PASSWORD;
+  return opts;
+}
+
+let _connection: IORedis | null = null;
+
+/** Lazily-created singleton ioredis connection. */
+export function getConnection(): IORedis {
+  if (!_connection) {
+    _connection = new IORedis(REDIS_URL, buildOptions());
+    _connection.on("error", (err) => {
+      // Log but don't crash the process on transient Redis errors.
+      console.error("[queue] redis error:", err.message);
+    });
+  }
+  return _connection;
+}
+
+export const BULLMQ_PREFIX = QUEUE_PREFIX;