feat: Add /tools page with centralized tool registry management

- Add ToolsPage for managing MCP tools activation and persistence
- Centralize all tool handlers in services/tools/handlers/
- toolRegistry.ts is now the single source of truth for tool state
- Add tools store for pinned tools (persisted in localStorage)
- Tools can be pinned to stay active across page navigation
- Remove old individual tool files, replaced by centralized handlers

frontend/src/components/Toolbar.vue

@@ -125,6 +125,12 @@ onMounted(() => {
           <line x1="12" y1="19" x2="20" y2="19"/>
         </svg>
       </RouterLink>
+
+      <RouterLink to="/tools" class="toolbar-btn" :class="{ active: route.path === '/tools' }" title="Tools">
+        <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+          <path d="M14.7 6.3a1 1 0 0 0 0 1.4l1.6 1.6a1 1 0 0 0 1.4 0l3.77-3.77a6 6 0 0 1-7.94 7.94l-6.91 6.91a2.12 2.12 0 0 1-3-3l6.91-6.91a6 6 0 0 1 7.94-7.94l-3.76 3.76z"/>
+        </svg>
+      </RouterLink>
     </div>
 
     <div class="toolbar-divider"></div>