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/handlers/bookmarks.go

@@ -318,6 +318,14 @@ func HandleBookmarksUpdate(w http.ResponseWriter, r *http.Request) {
 		respond(w, 0, nil, e)
 		return
 	}
+	// Review M-10: reject a stale base version BEFORE doing outbound preview
+	// work. The transaction below still re-checks under the user lock; this
+	// early check only avoids spending up to 8 seconds and the shared preview
+	// budget on a request that can only end in 409.
+	if stored, _ := existing["version"].(float64); int(stored) != baseVersion {
+		respond(w, 0, nil, conflict("Bookmark was modified elsewhere; reload to see the latest version"))
+		return
+	}
 	if s := str(d, "url"); s != "" && s != str(existing, "url") {
 		addPreview(r.Context(), previewKey(r), d, false)
 	}
@@ -400,7 +408,7 @@ func HandleBookmarksShare(w http.ResponseWriter, r *http.Request) {
 	if !ok {
 		return
 	}
-	list, e := ids(b, "userIds")
+	list, e := cappedIDs(b, "userIds", maxShareRecipients)
 	if e != nil {
 		respond(w, 0, nil, e)
 		return