fix(mcpb): add Windows support via platform_overrides and run.cmd

The previous manifest hardcoded /bin/sh which fails on Windows. Fix by:
- Adding mcpb/run.cmd: Windows batch wrapper that searches common uvx
  install locations (%USERPROFILE%\.local\bin, %LOCALAPPDATA%\uv\bin,
  %USERPROFILE%\.cargo\bin) before falling back to PATH, with a clear
  error message pointing to winget/PowerShell install instructions
- Adding platform_overrides.win32 in mcp_config to use cmd /c run.cmd
  on Windows while macOS/Linux continue using /bin/sh run.sh
- Expanding compatibility.platforms to include win32

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcpb/manifest.json

@@ -25,11 +25,17 @@
         "NEXTCLOUD_HOST": "${user_config.nextcloud_host}",
         "NEXTCLOUD_USERNAME": "${user_config.nextcloud_username}",
         "NEXTCLOUD_PASSWORD": "${user_config.nextcloud_password}"
+      },
+      "platform_overrides": {
+        "win32": {
+          "command": "cmd",
+          "args": ["/c", "${__dirname}/run.cmd"]
+        }
       }
     }
   },
   "compatibility": {
-    "platforms": ["darwin", "linux"]
+    "platforms": ["darwin", "linux", "win32"]
   },
   "tools_generated": true,
   "user_config": {