fix(audit-integrations): SMTP/PG/Socket.IO timeouts, prompt injection, secret-at-rest

A focused review of every external integration surfaced six issues the
original audit missed.  Fixed here.

HIGH
* Socket.IO had an unconditional 30-second idle disconnect on every
  socket.  The comment on the line acknowledged it was "for development
  only, would be longer in prod" but no NODE_ENV guard existed, and the
  `socket.onAny` listener only resets on inbound client events — every
  dashboard connection that received only server-push events would have
  been torn down every 30s in production.  Removed the manual idle
  timer entirely; Socket.IO's pingTimeout / pingInterval handles
  dead-transport detection at the protocol level.
* SMTP transporters had no `connectionTimeout` / `greetingTimeout` /
  `socketTimeout`.  Nodemailer's defaults are 2 minutes for connect
  and unlimited for socket — a hung SMTP server would have held a
  BullMQ `email` worker concurrency slot for up to 10 min per job
  (5 retries × 2 min).  Set 10s/10s/30s on both the system transporter
  in `src/lib/email/index.ts` and the user-account transporter in
  `email-compose.service.ts`.

MEDIUM
* PostgreSQL pool had no `statement_timeout` /
  `idle_in_transaction_session_timeout`.  A slow query or transaction
  held by a crashed handler would have eventually exhausted the
  20-connection pool.  30s statement cap, 10s idle-in-tx cap, plus
  `max_lifetime: 30min` to recycle connections.
* `umami_password` and `umami_api_token` were stored as plaintext in
  `system_settings` (the SMTP and S3 secret paths use AES-GCM).  The
  reader now passes them through `readSecret()` which auto-detects
  the encrypted `iv:cipher:tag` shape and decrypts, falling back to
  legacy plaintext so operators can rotate without a flag-day.
* AI email-draft worker interpolated `additionalInstructions` (user-
  controlled) directly into the OpenAI prompt — a hostile rep could
  close the instructions block and inject prompt directives that
  override the system prompt.  Added `sanitizeForPrompt()` that
  strips newlines + quote chars, caps at 500 chars, and the prompt
  now wraps the value in a "treat as data not commands" preamble.

LOW
* Legacy `ensureBucket()` in `src/lib/minio/index.ts` was unguarded —
  if any future code imported it (currently no callers), a misconfigured
  prod deploy could mint a fresh empty bucket.  Now matches the gate
  used by the pluggable S3Backend (`MINIO_AUTO_CREATE_BUCKET=true`
  required) so the legacy export and the new pluggable path agree.

Confirmed not-an-issue: BullMQ Workers create connections via
`{ url }` options object, and BullMQ sets `maxRetriesPerRequest: null`
internally for those — no fix needed.  The shared `redis` singleton
that does keep `maxRetriesPerRequest: 3` is used only for direct
Redis ops (rate-limit sliding window, etc.), never for blocking
BullMQ commands, so the value is correct there.

Test status: 1175/1175 vitest, tsc clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/socket/server.ts

@@ -149,15 +149,16 @@ export function initSocketServer(
       socket.leave(`${type}:${id}`);
     });
 
-    // Idle timeout (30 seconds - for development only, would be longer in prod)
-    let idleTimer = setTimeout(() => socket.disconnect(), 30_000);
-    socket.onAny(() => {
-      clearTimeout(idleTimer);
-      idleTimer = setTimeout(() => socket.disconnect(), 30_000);
-    });
+    // NOTE: there is no manual idle-disconnect timer here. The previous
+    // implementation forcibly disconnected every socket after 30s of
+    // client-emitted activity, which (a) would have torn down every
+    // dashboard connection in production every half minute (the server-
+    // push events don't reset the timer because `onAny` fires only on
+    // inbound messages from the client) and (b) was redundant — Socket.IO's
+    // built-in pingTimeout / pingInterval handles dead-transport detection
+    // at the protocol level.
 
     socket.on('disconnect', () => {
-      clearTimeout(idleTimer);
       logger.debug({ userId }, 'Socket disconnected');
     });
   });