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/digital-signatures/hooks/use-signatures.ts

@@ -1,31 +1,37 @@
-'use client';
+"use client";
 
-import { useState, useEffect, useCallback } from 'react';
-import { useStorage } from '@/core/storage';
-import { v4 as uuid } from 'uuid';
-import type { SignatureAsset, SignatureAssetType, AssetVersion } from '../types';
+import { useState, useEffect, useCallback } from "react";
+import { useStorage } from "@/core/storage";
+import { v4 as uuid } from "uuid";
+import type {
+  SignatureAsset,
+  SignatureAssetType,
+  AssetVersion,
+} from "../types";
 
-const PREFIX = 'sig:';
+const PREFIX = "sig:";
 
 export interface SignatureFilters {
   search: string;
-  type: SignatureAssetType | 'all';
+  type: SignatureAssetType | "all";
 }
 
 export function useSignatures() {
-  const storage = useStorage('digital-signatures');
+  const storage = useStorage("digital-signatures");
   const [assets, setAssets] = useState<SignatureAsset[]>([]);
   const [loading, setLoading] = useState(true);
-  const [filters, setFilters] = useState<SignatureFilters>({ search: '', type: 'all' });
+  const [filters, setFilters] = useState<SignatureFilters>({
+    search: "",
+    type: "all",
+  });
 
   const refresh = useCallback(async () => {
     setLoading(true);
-    const keys = await storage.list();
+    const all = await storage.exportAll();
     const results: SignatureAsset[] = [];
-    for (const key of keys) {
-      if (key.startsWith(PREFIX)) {
-        const item = await storage.get<SignatureAsset>(key);
-        if (item) results.push(item);
+    for (const [key, value] of Object.entries(all)) {
+      if (key.startsWith(PREFIX) && value) {
+        results.push(value as SignatureAsset);
       }
     }
     results.sort((a, b) => b.createdAt.localeCompare(a.createdAt));
@@ -34,53 +40,95 @@ export function useSignatures() {
   }, [storage]);
 
   // eslint-disable-next-line react-hooks/set-state-in-effect
-  useEffect(() => { refresh(); }, [refresh]);
+  useEffect(() => {
+    refresh();
+  }, [refresh]);
 
-  const addAsset = useCallback(async (data: Omit<SignatureAsset, 'id' | 'createdAt' | 'updatedAt'>) => {
-    const now = new Date().toISOString();
-    const asset: SignatureAsset = { ...data, id: uuid(), createdAt: now, updatedAt: now };
-    await storage.set(`${PREFIX}${asset.id}`, asset);
-    await refresh();
-    return asset;
-  }, [storage, refresh]);
+  const addAsset = useCallback(
+    async (data: Omit<SignatureAsset, "id" | "createdAt" | "updatedAt">) => {
+      const now = new Date().toISOString();
+      const asset: SignatureAsset = {
+        ...data,
+        id: uuid(),
+        createdAt: now,
+        updatedAt: now,
+      };
+      await storage.set(`${PREFIX}${asset.id}`, asset);
+      await refresh();
+      return asset;
+    },
+    [storage, refresh],
+  );
 
-  const updateAsset = useCallback(async (id: string, updates: Partial<SignatureAsset>) => {
-    const existing = assets.find((a) => a.id === id);
-    if (!existing) return;
-    const updated: SignatureAsset = {
-      ...existing, ...updates,
-      id: existing.id, createdAt: existing.createdAt,
-      updatedAt: new Date().toISOString(),
-    };
-    await storage.set(`${PREFIX}${id}`, updated);
-    await refresh();
-  }, [storage, refresh, assets]);
+  const updateAsset = useCallback(
+    async (id: string, updates: Partial<SignatureAsset>) => {
+      const existing = assets.find((a) => a.id === id);
+      if (!existing) return;
+      const updated: SignatureAsset = {
+        ...existing,
+        ...updates,
+        id: existing.id,
+        createdAt: existing.createdAt,
+        updatedAt: new Date().toISOString(),
+      };
+      await storage.set(`${PREFIX}${id}`, updated);
+      await refresh();
+    },
+    [storage, refresh, assets],
+  );
 
-  const addVersion = useCallback(async (assetId: string, imageUrl: string, notes: string) => {
-    const existing = assets.find((a) => a.id === assetId);
-    if (!existing) return;
-    const version: AssetVersion = { id: uuid(), imageUrl, notes, createdAt: new Date().toISOString() };
-    const updatedVersions = [...(existing.versions ?? []), version];
-    await updateAsset(assetId, { imageUrl, versions: updatedVersions });
-  }, [assets, updateAsset]);
+  const addVersion = useCallback(
+    async (assetId: string, imageUrl: string, notes: string) => {
+      const existing = assets.find((a) => a.id === assetId);
+      if (!existing) return;
+      const version: AssetVersion = {
+        id: uuid(),
+        imageUrl,
+        notes,
+        createdAt: new Date().toISOString(),
+      };
+      const updatedVersions = [...(existing.versions ?? []), version];
+      await updateAsset(assetId, { imageUrl, versions: updatedVersions });
+    },
+    [assets, updateAsset],
+  );
 
-  const removeAsset = useCallback(async (id: string) => {
-    await storage.delete(`${PREFIX}${id}`);
-    await refresh();
-  }, [storage, refresh]);
+  const removeAsset = useCallback(
+    async (id: string) => {
+      await storage.delete(`${PREFIX}${id}`);
+      await refresh();
+    },
+    [storage, refresh],
+  );
 
-  const updateFilter = useCallback(<K extends keyof SignatureFilters>(key: K, value: SignatureFilters[K]) => {
-    setFilters((prev) => ({ ...prev, [key]: value }));
-  }, []);
+  const updateFilter = useCallback(
+    <K extends keyof SignatureFilters>(key: K, value: SignatureFilters[K]) => {
+      setFilters((prev) => ({ ...prev, [key]: value }));
+    },
+    [],
+  );
 
   const filteredAssets = assets.filter((a) => {
-    if (filters.type !== 'all' && a.type !== filters.type) return false;
+    if (filters.type !== "all" && a.type !== filters.type) return false;
     if (filters.search) {
       const q = filters.search.toLowerCase();
-      return a.label.toLowerCase().includes(q) || a.owner.toLowerCase().includes(q);
+      return (
+        a.label.toLowerCase().includes(q) || a.owner.toLowerCase().includes(q)
+      );
     }
     return true;
   });
 
-  return { assets: filteredAssets, allAssets: assets, loading, filters, updateFilter, addAsset, updateAsset, addVersion, removeAsset, refresh };
+  return {
+    assets: filteredAssets,
+    allAssets: assets,
+    loading,
+    filters,
+    updateFilter,
+    addAsset,
+    updateAsset,
+    addVersion,
+    removeAsset,
+    refresh,
+  };
 }