perf: fix N+1 query pattern across all modules + rack numbering

CRITICAL PERF BUG: Every hook did storage.list() (1 HTTP call fetching ALL
items with values, discarding values, returning only keys) then storage.get()
for EACH key (N individual HTTP calls re-fetching values one by one).

With 6 entries + contacts + tags, Registratura page fired ~40 sequential
HTTP requests on load, where 3 would suffice.

Fix: Replace list()+N*get() with single exportAll() call in ALL hooks:
- registratura/registry-service.ts (added exportAll to RegistryStorage interface)
- address-book/use-contacts.ts
- it-inventory/use-inventory.ts
- password-vault/use-vault.ts
- word-templates/use-templates.ts
- prompt-generator/use-prompt-generator.ts
- hot-desk/use-reservations.ts
- email-signature/use-saved-signatures.ts
- digital-signatures/use-signatures.ts
- ai-chat/use-chat.ts
- core/tagging/tag-service.ts (uses storage.export())

Additional fixes:
- registratura/use-registry.ts: addEntry uses optimistic local state update
  instead of double-refresh; closeEntry batches saves with Promise.all +
  single refresh
- server-rack.tsx: reversed slot rendering so U1 is at bottom (standard
  rack numbering, per user's physical rack)

Performance impact: ~90% reduction in HTTP requests on page load for all modules

src/modules/registratura/services/registry-service.ts

@@ -8,17 +8,22 @@ export interface RegistryStorage {
   set<T>(key: string, value: T): Promise<void>;
   delete(key: string): Promise<void>;
   list(): Promise<string[]>;
+  exportAll(): Promise<Record<string, unknown>>;
 }
 
+/**
+ * Load all registry entries in a SINGLE request.
+ * Uses exportAll() which fetches namespace data in one HTTP call,
+ * avoiding the N+1 pattern (list keys → get each one individually).
+ */
 export async function getAllEntries(
   storage: RegistryStorage,
 ): Promise<RegistryEntry[]> {
-  const keys = await storage.list();
+  const all = await storage.exportAll();
   const entries: RegistryEntry[] = [];
-  for (const key of keys) {
-    if (key.startsWith(STORAGE_PREFIX)) {
-      const entry = await storage.get<RegistryEntry>(key);
-      if (entry) entries.push(entry);
+  for (const [key, value] of Object.entries(all)) {
+    if (key.startsWith(STORAGE_PREFIX) && value) {
+      entries.push(value as RegistryEntry);
     }
   }
   entries.sort((a, b) => b.createdAt.localeCompare(a.createdAt));