feat: Add source code viewer with Gitea integration

- Add /source page with file explorer and code viewer
- Connect to Gitea API for repository browsing
- Implement MCP tools: get_repo_info, list_repo_files, read_repo_file, search_repo_code
- Default to nucleo000/agent-ui repository
- Support branch switching and file search

frontend/src/components/Toolbar.vue

@@ -103,6 +103,13 @@ onMounted(() => {
           <path d="M3 12c0 1.66 4 3 9 3s9-1.34 9-3"/>
         </svg>
       </RouterLink>
+
+      <RouterLink to="/source" class="toolbar-btn" :class="{ active: route.path === '/source' }" title="Source Code">
+        <svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+          <polyline points="16 18 22 12 16 6"/>
+          <polyline points="8 6 2 12 8 18"/>
+        </svg>
+      </RouterLink>
     </div>
 
     <div class="toolbar-divider"></div>