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/verify-linux-appimage.test.mjs

@@ -21,7 +21,7 @@ const createPayload = () => {
   ].join('\n'));
   writeElf(path.join(root, 'openchamber'), 'x64');
   writeElf(path.join(root, 'resources/opencode-cli/opencode'), 'x64');
-  for (const name of ['better_sqlite3.node', 'pty.node', 'sherpa-onnx.node']) {
+  for (const name of ['pty.node', 'sherpa-onnx.node']) {
     writeElf(path.join(root, 'resources/app.asar.unpacked/node_modules', name), 'x64');
   }
   return root;
@@ -53,7 +53,7 @@ test('verifies identity, version, and native payload architecture', () => {
       expectedOpenCodeVersion: '1.17.18',
       runCliVersion: () => '1.17.18',
     });
-    assert.equal(result.nativeModuleCount, 3);
+    assert.equal(result.nativeModuleCount, 2);
   } finally {
     fs.rmSync(root, { recursive: true, force: true });
   }