feat: always show admin menu with online checks for operations

**Changes:**

1. **Admin menu always visible** (base.html)
   - Removed 'hidden' class from "Администратор цен" link
   - Menu no longer depends on write permission check
   - Users can access pricing/pricelists pages in offline mode

2. **Online status checks for mutations** (admin_pricing.html)
   - Added checkOnlineStatus() helper function
   - createPricelist() checks online before creating
   - deletePricelist() checks online before deleting
   - Clear user feedback when operations blocked offline

**User Impact:**
- Admin menu accessible in both online and offline modes
- View-only access to pricelists when offline
- Clear error messages when attempting mutations offline
- Better offline-first UX

Part of Phase 2.5: Full Offline Mode

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web/templates/admin_pricing.html

@@ -1032,7 +1032,23 @@ function closePricelistsCreateModal() {
     document.getElementById('pricelists-create-modal').classList.remove('flex');
 }
 
+async function checkOnlineStatus() {
+    try {
+        const resp = await fetch('/api/db-status');
+        const data = await resp.json();
+        return data.connected === true;
+    } catch(e) {
+        return false;
+    }
+}
+
 async function createPricelist() {
+    // Check if online before creating
+    const isOnline = await checkOnlineStatus();
+    if (!isOnline) {
+        throw new Error('Создание прайслистов доступно только в онлайн режиме');
+    }
+
     const resp = await fetch('/api/pricelists', {
         method: 'POST',
         headers: {
@@ -1050,6 +1066,13 @@ async function createPricelist() {
 }
 
 async function deletePricelist(id) {
+    // Check if online before deleting
+    const isOnline = await checkOnlineStatus();
+    if (!isOnline) {
+        showToast('Удаление прайслистов доступно только в онлайн режиме', 'error');
+        return;
+    }
+
     if (!confirm('Удалить этот прайслист?')) return;
 
     try {