feat(search): Meilisearch message search — indexer + permission-scoped query

New search module: a message index (Meilisearch, MEILI_URL-gated; no-op when unset),
a SearchProjector that indexes on message.sent, and a SearchService whose permission
fence runs server-side — a query only touches the caller's own scope AND the threads
they currently belong to (resolved live from participant rows, so membership changes
reflect immediately). Every conversation kind (chat/mail/sms) is a message with a TEXT
part, so all are searchable through one index. POST /v1/search + /reindex (backfill).
5 fence tests green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packages/iios-service/package.json

@@ -29,6 +29,7 @@
     "ioredis": "^5.11.1",
     "jsonwebtoken": "^9.0.3",
     "jwks-rsa": "^4.1.0",
+    "meilisearch": "^0.45.0",
     "nodemailer": "^9.0.3",
     "prisma": "^6.2.1",
     "reflect-metadata": "^0.2.2",