feat(mcp): add Model Context Protocol integration

Implement comprehensive MCP support with stdio/HTTP/SSE transports, environment variable configuration (env and envFile), custom headers, tool registration, and automatic resource cleanup. Includes full test coverage and VSCode-compatible configuration.

- Added pkg/mcp/manager.go for server lifecycle management
- Added pkg/tools/mcp_tool.go for tool wrapping
- Integrated into agent loop with cleanup
- Support for envFile loading (.env format)
- Headers injection for HTTP/SSE authentication
- Example configs for filesystem, github, brave-search, postgres

config/config.example.json

@@ -14,7 +14,9 @@
       "enabled": false,
       "token": "YOUR_TELEGRAM_BOT_TOKEN",
       "proxy": "",
-      "allow_from": ["YOUR_USER_ID"]
+      "allow_from": [
+        "YOUR_USER_ID"
+      ]
     },
     "discord": {
       "enabled": false,
@@ -115,6 +117,62 @@
         "api_key": "YOUR_BRAVE_API_KEY",
         "max_results": 5
       }
+    },
+    "mcp": {
+      "enabled": false,
+      "servers": {
+        "filesystem": {
+          "enabled": false,
+          "command": "npx",
+          "args": [
+            "-y",
+            "@modelcontextprotocol/server-filesystem",
+            "/tmp"
+          ],
+          "env": {}
+        },
+        "github": {
+          "enabled": false,
+          "command": "npx",
+          "args": [
+            "-y",
+            "@modelcontextprotocol/server-github"
+          ],
+          "env": {
+            "GITHUB_PERSONAL_ACCESS_TOKEN": "YOUR_GITHUB_TOKEN"
+          },
+          "envFile": ".env"
+        },
+        "brave-search": {
+          "enabled": false,
+          "command": "npx",
+          "args": [
+            "-y",
+            "@modelcontextprotocol/server-brave-search"
+          ],
+          "env": {
+            "BRAVE_API_KEY": "YOUR_BRAVE_API_KEY"
+          }
+        },
+        "postgres": {
+          "enabled": false,
+          "command": "npx",
+          "args": [
+            "-y",
+            "@modelcontextprotocol/server-postgres",
+            "postgresql://user:password@localhost/dbname"
+          ]
+        },
+        "remote-http-example": {
+          "enabled": false,
+          "url": "https://mcp-server.example.com/stream",
+          "type": "sse",
+          "headers": {
+            "Authorization": "Bearer YOUR_TOKEN",
+            "X-Custom-Header": "custom-value"
+          }
+        }
+      }
     }
   },
   "heartbeat": {
@@ -129,4 +187,4 @@
     "host": "0.0.0.0",
     "port": 18790
   }
-}
+}