chore(deps): drop better-sqlite3 and its desktop packaging support

The SQLite write into OpenCode's database was the only consumer of
better-sqlite3 in the repository. Everything that existed to ship its native
binary went with it:

- the dependency in @openchamber/web and @openchamber/electron
- the afterPack hook staging better_sqlite3.node into app.asar.unpacked
- a dedicated @electron/rebuild pass (onlyModules) and its binary assertion,
  so desktop packaging now runs one native rebuild instead of two
- the bundler external entry and the AppImage required-native-module check

Desktop packaging, the AppImage verification tests, and the extension bundle
were re-validated after a clean reinstall, so no stale module could satisfy a
missed import.

packages/electron/package.json

@@ -8,7 +8,6 @@
   "main": "./dist-bundle/main.mjs",
   "dependencies": {
     "@openchamber/web": "workspace:*",
-    "better-sqlite3": "^12.10.0",
     "electron-context-menu": "^4.1.2",
     "electron-log": "^5.4.3",
     "electron-updater": "^6.8.3"