Address code review findings across API, web and deployment

High severity:
- wire TRUSTED_PROXY through Compose/deploy/docs and warn at web startup
- bucket public rate limits on effective client IP, add per-bookmark budget,
  and forward the signed browser identity from the share page
- disable first-run bootstrap in server deployments and document seeding
- serialize last-admin demotion in one advisory-locked transaction

Medium/low:
- cap and batch share recipient inserts
- add a shared outbound budget for preview/CardDAV/IMAP/signal work
- pin CardDAV dials to 443 and bound IMAP logout
- fix rightward kanban column drags and normalize cards on column delete
- classify backend outages in auth guards, add request timeouts and an
  error boundary, remove the dead login route, surface throttling
- enforce pinned/unpinned page reorder grouping server-side
- avoid preview work for stale bookmark versions; drop duplicate dialog fetch
- sequence-guard collection/tag/calendar/quick-find loads
- validate property config and fix MULTI_SELECT/DATE filter inputs
- document index maintenance; apply same-origin check to sign-out
- trim signup names, unique shared dates and kanban keys (migration 010),
  reset reference cache on identity changes, hide OIDC issuer, return 413
  for oversized direct bodies, escape Markdown link destinations
- remove dead template files and duplicate test helper

Verified with go build/vet, full PostgreSQL race suite, db convergence,
tsc, both ESLint configs and a Next production build.

web/app/(app)/admin/client.tsx

@@ -4,6 +4,7 @@ import { useEffect, useState } from 'react'
 import { toast } from 'sonner'
 import { Eye, Shield } from 'lucide-react'
 import { Button } from '@/components/ui/button'
+import { resetReferenceCache } from '@/lib/reference-data'
 
 type U = { id: string; name: string | null; email: string; role: string; _count?: { bookmarks: number; pages: number; tags: number } }
 
@@ -21,6 +22,8 @@ export function AdminClient({ currentUserId }: { currentUserId: string }) {
   const viewAs = async (userId: string) => {
     const res = await fetch('/api/admin/view-as', { method: 'POST', headers: { 'Content-Type': 'application/json' }, body: JSON.stringify({ userId }) })
     if (!res.ok) return toast.error('Could not switch account')
+    // Review L-6: entering view-as changes the effective identity.
+    resetReferenceCache()
     window.location.href = '/pages'
   }