feat(android): replace WebView with tested native Compose API slice

Add real native onboarding/auth/dashboard/tasks/notes/shopping, origin-bound HTTPS and encrypted AndroidKeyStore session persistence. Archive the superseded browser renderer and tests. Verify 10 JVM tests, 6 native API-35 emulator tests, lintDebug/lintRelease and debug/unsigned release APK/AAB builds; the real upstream suite passes 7 tests and exports a nonblank native fixture screenshot. Tink host-tool update removes the old generated-protobuf warning. Full module/visual parity remains explicitly incomplete.

legacy/README.md

@@ -0,0 +1,8 @@
+# Superseded WebView prototype
+
+These files are retained as historical reference, not shipped application code.
+The Android browser tests in `legacy/android/tests` and Apple BrowserModel tests
+describe this prototype, not native feature parity.
+Android now selects the explicitly named native test source directories instead.
+Do not restore a WebView as the application surface or count old browser tests as
+native-client validation.