Add GitHub Pages landing page and fix electron-builder config

- Create docs/ landing page with dark theme, download link, features,
  setup instructions, and requirements
- Fix build config: add signAndEditExecutable=false to avoid winCodeSign
  symlink errors, replace broken afterSign/afterAllArtifactBuild with
  forceCodeSigning=false
- Clean up removed dev dependencies (sharp, png-to-ico) from lockfile

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

package.json

@@ -18,13 +18,13 @@
     },
     "win": {
       "target": "portable",
-      "icon": "assets/icon.png"
+      "icon": "assets/icon.png",
+      "signAndEditExecutable": false
     },
     "portable": {
       "artifactName": "AltaCameraProxy-${version}-portable.exe"
     },
-    "afterSign": false,
-    "afterAllArtifactBuild": false
+    "forceCodeSigning": false
   },
   "keywords": [
     "electron",
@@ -37,9 +37,7 @@
   "devDependencies": {
     "electron": "^28.0.0",
     "electron-builder": "^26.4.0",
-    "electron-packager": "^17.1.2",
-    "png-to-ico": "^3.0.1",
-    "sharp": "^0.34.5"
+    "electron-packager": "^17.1.2"
   },
   "dependencies": {
     "axios": "^1.6.0",