fix: vault home recursive + backup viewer fixes + AI status at startup

- Vault home (#12): recursive file listing (rglob), rel_dir in metadata,
  'recursif' badge, updated roadmap description
- Backup viewer: fix close button (inline onclick + event delegation
  fallback for text nodes), improve error messages
- Backup API: remove response_model to prevent Pydantic 500 errors,
  add try/except + logging on backups/diff/restore endpoints,
  per-entry error handling in _list_backup_files,
  encoding safety (errors='replace') on read_text
- AI status: call /api/ai/status at startup in _initAIStatus
  instead of waiting for user click on sync badge

frontend/style.css

@@ -4071,6 +4071,17 @@ body.resizing-v {
   border-radius: 4px;
 }
 
+.vault-home-recursive-badge {
+  font-size: 0.7rem;
+  font-weight: 600;
+  color: var(--accent);
+  background: color-mix(in srgb, var(--accent) 12%, transparent);
+  padding: 2px 8px;
+  border-radius: 4px;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+}
+
 .vault-home-dir-info {
   font-size: 0.75rem;
   color: var(--text-muted);