build: bundle sharp's win32-x64 prebuilt for Windows packaging

The packaged installer-rp crashed on launch with
"Could not load the 'sharp' module using the win32-x64 runtime" because
electron-builder ran on Linux and only the Linux sharp variants were
present in node_modules.

- Add `preinstall:sharp-win32` script that force-installs
  `@img/sharp-win32-x64@0.34.5` into the local node_modules (npm refuses
  it on Linux without --force due to its os/cpu restrictions).
- Chain that script before both `dist:win` and `dist:win:rp` so future
  Windows builds always have the native prebuilt available.
- Exclude `@img/sharp-{,libvips-}linux*` from the packaged files list in
  both electron-builder configs so the unused Linux variants don't bloat
  the portable exe.

Verified `release/win-unpacked/resources/app.asar.unpacked/node_modules/
@img/sharp-win32-x64/lib/sharp-win32-x64.node` is present and that no
linux sharp variants ship inside the asar.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

package.json

@@ -9,8 +9,9 @@
     "dev:server": "tsc -p tsconfig.server.json && node dist/server/app.js",
     "installer": "tsc -p tsconfig.installer.json && electron .",
     "installer:rp": "tsc -p tsconfig.installer-rp.json && electron dist/installer-rp/main.js",
-    "dist:win": "tsc -p tsconfig.installer.json && electron-builder --win --config electron-builder.yml",
-    "dist:win:rp": "tsc -p tsconfig.installer-rp.json && electron-builder --win --config electron-builder-rp.yml"
+    "preinstall:sharp-win32": "npm install --no-save --force @img/sharp-win32-x64@0.34.5",
+    "dist:win": "npm run preinstall:sharp-win32 && tsc -p tsconfig.installer.json && electron-builder --win --config electron-builder.yml",
+    "dist:win:rp": "npm run preinstall:sharp-win32 && tsc -p tsconfig.installer-rp.json && electron-builder --win --config electron-builder-rp.yml"
   },
   "dependencies": {
     "@types/archiver": "^7.0.0",