fix(mcp): declare TIMEBOOK_API_URL/TIMEBOOK_WEB_URL env vars in server.json

The README documents these as supported overrides for self-hosted/local-dev
Timebook setups, but the server.json registry entry didn't declare them, so
MCP clients reading the registry had no way to know they exist or surface
them in their UIs. Adding both as optional, non-secret string env vars.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ktamas77

server.json

@@ -21,6 +21,22 @@
           "type": "positional",
           "value": "mcp"
         }
+      ],
+      "environmentVariables": [
+        {
+          "name": "TIMEBOOK_API_URL",
+          "description": "Override the Timebook API base URL. Defaults to https://usetimebook.com.",
+          "isRequired": false,
+          "isSecret": false,
+          "format": "string"
+        },
+        {
+          "name": "TIMEBOOK_WEB_URL",
+          "description": "Override the Timebook web URL used during `timebook login`. Defaults to https://usetimebook.com.",
+          "isRequired": false,
+          "isSecret": false,
+          "format": "string"
+        }
       ]
     }
   ]