feat(python-runtime): package the Windows x64 dsh executable

Add node24-win-x64 as the only supported Windows runtime target and publish it as a py3-none-win_amd64 wheel containing the conventional dsh and ripgrep .exe payload names. Keep Windows ARM64 rejected explicitly so Python cannot claim a carrier that CI and release automation do not build.

Teach the pkg builder to require a native x64 Windows host, validate both node-pty ConPTY addons, copy @vscode's win32 ripgrep executable, and recognize pkg's .exe output. Extend runtime resolution, wheel staging, payload validation, and the preset closure check so the Windows-specific PowerShell plugins and sidecars fail loud when omitted.

The sidecar resolver now maps a packaged main.exe to main-rg.exe; focused TypeScript and Python tests cover that name, the win_amd64 manifest, x64-only host selection, complete wheel payload, ConPTY inventory, and platform-conditioned plugin closure.

python/sdk-runtime/platforms.json

@@ -10,5 +10,9 @@
   "macos-arm64": {
     "tag": "macosx_14_0_arm64",
     "executable": "deepseek-harness-sdk-runtime-macos-arm64"
+  },
+  "win-x64": {
+    "tag": "win_amd64",
+    "executable": "deepseek-harness-sdk-runtime-win-x64.exe"
   }
 }