feat(04-01): register runtime variables, extend VaultTab, add DB query, create template groups

- Register 96 runtime variables in variableRegistry for autocomplete/validation
- Extend VaultTab type to include 'prompts' for prompt editor tab
- Add getPackUsageCount() to DatabaseService for pack usage badges
- Create templateGroups.ts with 7 groups covering all 41 templates
- Fix VaultPanel.svelte to import VaultTab type instead of local redeclaration

src/lib/services/database.ts

@@ -2644,6 +2644,15 @@ class DatabaseService {
     return results[0].count === 0
   }
 
+  async getPackUsageCount(packId: string): Promise<number> {
+    const db = await this.getDb()
+    const results = await db.select<any[]>(
+      'SELECT COUNT(*) as count FROM stories WHERE pack_id = ?',
+      [packId],
+    )
+    return results[0].count
+  }
+
   // ===== Pack Template Operations =====
 
   async getPackTemplates(packId: string): Promise<PackTemplate[]> {