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/ai-chat/hooks/use-chat.ts

@@ -1,14 +1,14 @@
-'use client';
+"use client";
 
-import { useState, useEffect, useCallback } from 'react';
-import { useStorage } from '@/core/storage';
-import { v4 as uuid } from 'uuid';
-import type { ChatMessage, ChatSession } from '../types';
+import { useState, useEffect, useCallback } from "react";
+import { useStorage } from "@/core/storage";
+import { v4 as uuid } from "uuid";
+import type { ChatMessage, ChatSession } from "../types";
 
-const SESSION_PREFIX = 'session:';
+const SESSION_PREFIX = "session:";
 
 export function useChat() {
-  const storage = useStorage('ai-chat');
+  const storage = useStorage("ai-chat");
   const [sessions, setSessions] = useState<ChatSession[]>([]);
   const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
   const [loading, setLoading] = useState(true);
@@ -17,12 +17,11 @@ export function useChat() {
 
   const refresh = useCallback(async () => {
     setLoading(true);
-    const keys = await storage.list();
+    const all = await storage.exportAll();
     const results: ChatSession[] = [];
-    for (const key of keys) {
-      if (key.startsWith(SESSION_PREFIX)) {
-        const session = await storage.get<ChatSession>(key);
-        if (session) results.push(session);
+    for (const [key, value] of Object.entries(all)) {
+      if (key.startsWith(SESSION_PREFIX) && value) {
+        results.push(value as ChatSession);
       }
     }
     results.sort((a, b) => b.createdAt.localeCompare(a.createdAt));
@@ -31,49 +30,65 @@ export function useChat() {
   }, [storage]);
 
   // eslint-disable-next-line react-hooks/set-state-in-effect
-  useEffect(() => { refresh(); }, [refresh]);
+  useEffect(() => {
+    refresh();
+  }, [refresh]);
 
-  const createSession = useCallback(async (title?: string) => {
-    const session: ChatSession = {
-      id: uuid(),
-      title: title || `Conversație ${new Date().toLocaleDateString('ro-RO')}`,
-      messages: [],
-      createdAt: new Date().toISOString(),
-    };
-    await storage.set(`${SESSION_PREFIX}${session.id}`, session);
-    setSessions((prev) => [session, ...prev]);
-    setActiveSessionId(session.id);
-    return session;
-  }, [storage]);
+  const createSession = useCallback(
+    async (title?: string) => {
+      const session: ChatSession = {
+        id: uuid(),
+        title: title || `Conversație ${new Date().toLocaleDateString("ro-RO")}`,
+        messages: [],
+        createdAt: new Date().toISOString(),
+      };
+      await storage.set(`${SESSION_PREFIX}${session.id}`, session);
+      setSessions((prev) => [session, ...prev]);
+      setActiveSessionId(session.id);
+      return session;
+    },
+    [storage],
+  );
 
-  const addMessage = useCallback(async (content: string, role: ChatMessage['role']) => {
-    if (!activeSessionId) return;
-    const message: ChatMessage = {
-      id: uuid(),
-      role,
-      content,
-      timestamp: new Date().toISOString(),
-    };
-    setSessions((prev) => prev.map((s) => {
-      if (s.id !== activeSessionId) return s;
-      return { ...s, messages: [...s.messages, message] };
-    }));
-    // Persist
-    const current = sessions.find((s) => s.id === activeSessionId);
-    if (current) {
-      const updated = { ...current, messages: [...current.messages, message] };
-      await storage.set(`${SESSION_PREFIX}${activeSessionId}`, updated);
-    }
-    return message;
-  }, [storage, activeSessionId, sessions]);
+  const addMessage = useCallback(
+    async (content: string, role: ChatMessage["role"]) => {
+      if (!activeSessionId) return;
+      const message: ChatMessage = {
+        id: uuid(),
+        role,
+        content,
+        timestamp: new Date().toISOString(),
+      };
+      setSessions((prev) =>
+        prev.map((s) => {
+          if (s.id !== activeSessionId) return s;
+          return { ...s, messages: [...s.messages, message] };
+        }),
+      );
+      // Persist
+      const current = sessions.find((s) => s.id === activeSessionId);
+      if (current) {
+        const updated = {
+          ...current,
+          messages: [...current.messages, message],
+        };
+        await storage.set(`${SESSION_PREFIX}${activeSessionId}`, updated);
+      }
+      return message;
+    },
+    [storage, activeSessionId, sessions],
+  );
 
-  const deleteSession = useCallback(async (id: string) => {
-    await storage.delete(`${SESSION_PREFIX}${id}`);
-    setSessions((prev) => prev.filter((s) => s.id !== id));
-    if (activeSessionId === id) {
-      setActiveSessionId(null);
-    }
-  }, [storage, activeSessionId]);
+  const deleteSession = useCallback(
+    async (id: string) => {
+      await storage.delete(`${SESSION_PREFIX}${id}`);
+      setSessions((prev) => prev.filter((s) => s.id !== id));
+      if (activeSessionId === id) {
+        setActiveSessionId(null);
+      }
+    },
+    [storage, activeSessionId],
+  );
 
   const selectSession = useCallback((id: string) => {
     setActiveSessionId(id);