feat: add tools API endpoint and tools-selector form type

Backend:
- Add GET /api/v1/tools — list all available tools (plugin + MCP)
- Add GET /api/v1/tools/<tool_name> — get specific tool details

Frontend:
- Add TOOLS_SELECTOR form type for plugin config forms
- Multi-select dialog with tool name and description
- Add PluginTool entity type and API client methods

src/langbot/pkg/api/http/controller/groups/resources/tools.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import quart
+
+from ... import group
+
+
+@group.group_class('tools', '/api/v1/tools')
+class ToolsRouterGroup(group.RouterGroup):
+    async def initialize(self) -> None:
+        @self.route('', methods=['GET'], auth_type=group.AuthType.USER_TOKEN)
+        async def _() -> str:
+            """获取所有可用工具列表"""
+            tools = await self.ap.tool_mgr.get_all_tools()
+
+            tool_list = []
+            for tool in tools:
+                tool_list.append({
+                    'name': tool.name,
+                    'description': tool.description,
+                    'human_desc': tool.human_desc,
+                    'parameters': tool.parameters,
+                })
+
+            return self.success(data={'tools': tool_list})
+
+        @self.route('/<tool_name>', methods=['GET'], auth_type=group.AuthType.USER_TOKEN)
+        async def _(tool_name: str) -> str:
+            """获取特定工具详情"""
+            tools = await self.ap.tool_mgr.get_all_tools()
+
+            for tool in tools:
+                if tool.name == tool_name:
+                    return self.success(data={
+                        'tool': {
+                            'name': tool.name,
+                            'description': tool.description,
+                            'human_desc': tool.human_desc,
+                            'parameters': tool.parameters,
+                        }
+                    })
+
+            return self.http_status(404, -1, f'Tool not found: {tool_name}')