chore: merge main branch into mcp-tools-support

Resolved conflicts in:
- config/config.example.json: Added empty MCP config block
- pkg/config/config.go: Added MCP config structures to new ToolsConfig
- pkg/agent/loop.go: Integrated MCP tools with new AgentRegistry architecture

MCP tools now register to all agents in the registry during startup.

config/config.example.json

@@ -79,7 +79,8 @@
     },
     "openai": {
       "api_key": "",
-      "api_base": ""
+      "api_base": "",
+      "web_search": true
     },
     "openrouter": {
       "api_key": "sk-or-v1-xxx",
@@ -117,66 +118,23 @@
   },
   "tools": {
     "web": {
-      "search": {
+      "brave": {
+        "enabled": false,
         "api_key": "YOUR_BRAVE_API_KEY",
         "max_results": 5
+      },
+      "perplexity": {
+        "enabled": false,
+        "api_key": "pplx-xxx",
+        "max_results": 5
       }
     },
+    "cron": {
+      "exec_timeout_minutes": 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"
-          }
-        }
-      }
+      "servers": {}
     }
   },
   "heartbeat": {