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>

pnpm-lock.yaml

@@ -415,6 +415,9 @@ importers:
       jwks-rsa:
         specifier: ^4.1.0
         version: 4.1.0
+      meilisearch:
+        specifier: ^0.45.0
+        version: 0.45.0
       nodemailer:
         specifier: ^9.0.3
         version: 9.0.3
@@ -2715,6 +2718,9 @@ packages:
     resolution: {integrity: sha512-aisnrDP4GNe06UcKFnV5bfMNPBUw4jsLGaWwWfnH3v02GnBuXX2MCVn5RbrWo0j3pczUilYblq7fQ7Nw2t5XKw==}
     engines: {node: '>= 0.8'}
 
+  meilisearch@0.45.0:
+    resolution: {integrity: sha512-+zCzEqE+CumY4icB0Vox180adZqaNtnr60hJWGiEdmol5eWmksfY8rYsTcz87styXC2ZOg+2yF56gdH6oyIBTA==}
+
   memfs@3.5.3:
     resolution: {integrity: sha512-UERzLsxzllchadvbPs5aolHh65ISpKpM+ccLbOJ8/vvpBKmAWf+la7dXFy7Mr0ySHbdHrFv5kGFCUHHe6GFEmw==}
     engines: {node: '>= 4.0.0'}
@@ -5902,6 +5908,8 @@ snapshots:
 
   media-typer@1.1.0: {}
 
+  meilisearch@0.45.0: {}
+
   memfs@3.5.3:
     dependencies:
       fs-monkey: 1.1.0