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/scripts/rebuild-native.mjs

@@ -133,19 +133,6 @@ const ensureWindowsNodeAddonApiForNodePty = async (rebuildRootPath) => {
 
 console.log(`[electron] rebuilding native modules against Electron ${electronVersion}...`);
 
-await rebuild({
-  buildPath: electronDir,
-  electronVersion,
-  force: true,
-  arch: targetArchitecture.electronBuilder,
-  onlyModules: ['better-sqlite3'],
-});
-const betterSqliteDir = path.dirname(require.resolve('better-sqlite3/package.json'));
-const betterSqliteBinary = path.join(betterSqliteDir, 'build', 'Release', 'better_sqlite3.node');
-if (!existsSync(betterSqliteBinary)) {
-  throw new Error(`better-sqlite3 rebuild did not produce ${betterSqliteBinary}`);
-}
-
 // Rebuild against the hoisted root node_modules (bun workspace layout).
 // force=true re-links regardless of cached state; prebuild-install lookup is
 // bypassed by @electron/rebuild in favor of direct node-gyp builds.