fix(audit-tier-1): timeouts, lifecycle, per-port Documenso, FK constraints

Closes the second wave of HIGH-priority audit findings:

* fetchWithTimeout helper (new src/lib/fetch-with-timeout.ts) wraps
  Documenso, OCR, currency, Umami, IMAP, etc. — a hung upstream can
  no longer pin a worker concurrency slot indefinitely.  OpenAI client
  passes timeout: 30_000.  ImapFlow gets socket / greeting / connection
  timeouts.
* SIGTERM / SIGINT handler in src/server.ts drains in-flight HTTP,
  closes Socket.io, and disconnects Redis before exit; compose
  stop_grace_period bumped to 30s.  Adds closeSocketServer() helper.
* env.ts gains zod-validated PORT and MULTI_NODE_DEPLOYMENT, and
  filesystem.ts now reads from env (a typo can no longer silently
  disable the multi-node guard).
* Per-port Documenso template + recipient IDs land in system_settings
  with env fallback (PortDocumensoConfig now exposes eoiTemplateId,
  clientRecipientId, developerRecipientId, approvalRecipientId).
  document-templates.ts uses the per-port config and threads portId
  into documensoGenerateFromTemplate().
* Migration 0042 wires the eleven HIGH-tier missing FK constraints
  (documents/files/interests/reminders/berth_waiting_list/
  form_submissions) plus polymorphic CHECK round 2
  (yacht_ownership_history.owner_type, document_sends.document_kind),
  invoices.billing_entity_id NOT EMPTY, and clients.merged_into self-FK.
  Drizzle schema columns updated to .references(...) where possible
  so the misleading "FK wired in relations.ts" comments are gone.

Test status: 1168/1168 vitest, tsc clean.

Refs: docs/audit-comprehensive-2026-05-05.md HIGH §§5,6,7,8,9,10 +
MED §§14,15,16,18.

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

src/lib/db/schema/interests.ts

@@ -13,6 +13,7 @@ import { sql } from 'drizzle-orm';
 import { ports } from './ports';
 import { clients } from './clients';
 import { berths } from './berths';
+import { yachts } from './yachts';
 
 // Pipeline stages: open, details_sent, in_communication, eoi_sent, eoi_signed, deposit_10pct, contract_sent, contract_signed, completed
 
@@ -28,7 +29,7 @@ export const interests = pgTable(
     clientId: text('client_id')
       .notNull()
       .references(() => clients.id),
-    yachtId: text('yacht_id'), // FK added via relation; nullable until pipeline leaves 'open'
+    yachtId: text('yacht_id').references(() => yachts.id, { onDelete: 'set null' }),
     pipelineStage: text('pipeline_stage').notNull().default('open'),
     leadCategory: text('lead_category'), // general_interest, specific_qualified, hot_lead
     source: text('source'), // website, manual, referral, broker