chore(mcp): disable blender-mcp server telemetry

Upstream's update added telemetry that is on by default. Sets the three
opt-out env vars on the blender server in .mcp.json, which also suppresses
the consent prompt it would otherwise raise through the MCP client.

Documents the addon-side 'Allow Telemetry' preference as a separate switch:
it defaults to on, covers prompts, code snippets, screenshots and trajectory
data, and lives inside Blender where these env vars cannot reach it.

.mcp.json

@@ -9,7 +9,12 @@
     },
     "blender": {
       "command": "uv",
-      "args": ["run", "--project", "mcp/blender-mcp", "blender-mcp"]
+      "args": ["run", "--project", "mcp/blender-mcp", "blender-mcp"],
+      "env": {
+        "DISABLE_TELEMETRY": "1",
+        "BLENDER_MCP_DISABLE_TELEMETRY": "1",
+        "MCP_DISABLE_TELEMETRY": "1"
+      }
     }
   }
 }