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.

internal/db/bookmarks.go

@@ -23,7 +23,10 @@ const BookmarkOwnerView = `to_jsonb(b) || jsonb_build_object(
 // readers: the link itself, its presentation metadata, the content the owner
 // attached for readers (description, notes, due date, tags), and enough owner
 // identity to attribute the share inside the workspace. No contact record, no
-// recipient list, no alerts, no mailbox-watch settings, no board placement.
+// recipient list, no alerts, no mailbox-watch settings, no board placement
+// (kanbanColumnId/kanbanPosition). The legacy kanbanStatus badge IS included
+// deliberately: it is status, not placement, and API.md/web/AGENTS.md say so
+// (review L-10).
 const BookmarkSharedView = `jsonb_build_object(
  'id',b.id,'url',b.url,'title',b.title,'description',b.description,'notes',b.notes,
  'favicon',b.favicon,'ogImage',b."ogImage",'ogTitle',b."ogTitle",'ogDescription',b."ogDescription",