Merge sideloading, install links and devkit pairing

Combines the three feature branches on bundle-deps. Conflicts in server.py,
index.html, preload.js, README and test_server.py keep both sides. The
web-install downloader now uses urllib's default HTTPS context, so the
bundled CA list from 770f26c applies to it on Windows too.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

app/package.json

@@ -21,6 +21,14 @@
   "build": {
     "appId": "com.saphid.frame-control",
     "productName": "Frame Control",
+    "protocols": [
+      {
+        "name": "Frame Control install link",
+        "schemes": [
+          "frame-control"
+        ]
+      }
+    ],
     "directories": {
       "output": "dist",
       "buildResources": "build"
@@ -28,6 +36,7 @@
     "files": [
       "main.js",
       "preload.js",
+      "install-link.js",
       "package.json",
       "build/icon.png"
     ],