feat: Add epic_close MCP tool

- New epic_close(id) function to mark epics as completed
- Added tool definition and handler
- Usage: epic_close({ id: 'CF-E1' })

Task: CF-258

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

src/tools/index.ts

@@ -197,6 +197,17 @@ export const toolDefinitions = [
       required: ['task_id', 'epic_id'],
     },
   },
+  {
+    name: 'epic_close',
+    description: 'Close an epic (mark as completed)',
+    inputSchema: {
+      type: 'object',
+      properties: {
+        id: { type: 'string', description: 'Epic ID to close (e.g., VPN-E1, ST-E3)' },
+      },
+      required: ['id'],
+    },
+  },
 
   // Delegation Tools
   {