feat(flutter-cursor-templates): introduce MCP integration and conventions in project brief

- Added optional MCP integration settings in project-brief.yaml, allowing for environment-based server configurations.
- Introduced conventions for strict package imports to enhance code organization and maintainability.
- Updated brief schema to validate new MCP properties and ensure correct usage.
- Implemented MCP JSON builder to generate .cursor/mcp.json based on project brief settings.
- Enhanced resolver to include MCP configuration in generated files when enabled.

This update improves integration capabilities and enforces coding standards across the project.

flutter-cursor-templates/generator/brief-schema.json

@@ -162,6 +162,38 @@
       "type": "boolean",
       "description": "Pillar 6: Opt-in local telemetry for rule trigger analytics",
       "default": false
+    },
+    "integrations": {
+      "type": "object",
+      "description": "Optional third-party integrations for generated Cursor config",
+      "properties": {
+        "mcp": {
+          "type": "object",
+          "properties": {
+            "enabled": {
+              "type": "boolean",
+              "default": false,
+              "description": "When true, emit .cursor/mcp.json with env-placeholder server stubs only"
+            },
+            "preset": {
+              "type": "string",
+              "enum": ["auto", "minimal"],
+              "default": "auto",
+              "description": "minimal = empty mcpServers; auto = brief-derived stubs (still no committed secrets)"
+            }
+          }
+        }
+      }
+    },
+    "conventions": {
+      "type": "object",
+      "properties": {
+        "strict_package_imports": {
+          "type": "boolean",
+          "default": false,
+          "description": "When true, flutter-core rule enforces package: imports across feature boundaries"
+        }
+      }
     }
   }
 }