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/lib/api.ts

@@ -24,6 +24,21 @@ export const signClientIP = (ip: string): { ts: string; sig: string } => {
   return { ts, sig: createHmac('sha256', secret).update(`${ip}|${ts}`).digest('hex') }
 }
 
+// Review H-2: server-rendered pages that call Go directly (the public share
+// page) must forward the same attested identity as the data proxy, otherwise
+// every rendered share view lands in the web container's bucket. Returns an
+// empty object when there is no trusted proxy or no usable header.
+export const forwardedClientHeaders = (source: Headers): Record<string, string> => {
+  const ip = observedClientIP(source)
+  if (!ip) return {}
+  const { ts, sig } = signClientIP(ip)
+  return {
+    'x-computer-client-ip': ip,
+    'x-computer-client-ts': ts,
+    'x-computer-client-sig': sig,
+  }
+}
+
 // Only this trusted Next server signs assertions. The browser never chooses a
 // user ID, and Go still re-reads roles/ownership on every request. The typ
 // claim binds the token to the Bearer channel; Go rejects it as a cookie and
@@ -55,5 +70,18 @@ export async function backendFetch(path: string, init: RequestInit = {}) {
   }
   const viewAs = (await cookies()).get('computer_view_as')?.value
   if (viewAs) headers.set('Cookie', `computer_view_as=${encodeURIComponent(viewAs)}`)
-  return fetch(`${apiBase()}${path}`, { ...init, headers, cache: 'no-store' })
+  // Review M-7: bound server-side calls so a hung or blackholed backend
+  // cannot stall a route/server component until the platform timeout.
+  // Callers may provide their own signal to override this default.
+  const signal = init.signal ?? AbortSignal.timeout(10_000)
+  try {
+    return await fetch(`${apiBase()}${path}`, { ...init, headers, cache: 'no-store', signal })
+  } catch (error) {
+    if (error instanceof Error && error.name === 'TimeoutError') {
+      const timeout = new Error('Backend request timed out') as Error & { status?: number }
+      timeout.status = 504
+      throw timeout
+    }
+    throw error
+  }
 }