feat(install): add Windows PowerShell installer and copy buttons on site

Add install.ps1 mirroring install.sh for Windows: arch detection,
release zip download, binary extraction, user PATH update.

- copy install.ps1 to site public/ at build time (copy-install.mjs)
- serve /install.ps1 with text/plain Content-Type (vercel.json)
- add PowerShell one-liner to install page and README
- bump install.ps1 default version in bump_version.sh
- add CopyButton component next to every install command line

site/vercel.json

@@ -17,6 +17,10 @@
     {
       "source": "/install.sh",
       "headers": [{ "key": "Content-Type", "value": "text/x-shellscript; charset=utf-8" }]
+    },
+    {
+      "source": "/install.ps1",
+      "headers": [{ "key": "Content-Type", "value": "text/plain; charset=utf-8" }]
     }
   ]
 }