Migrate CI from Taskfile to Dagger

- Add Dagger to flake.nix
- Create Dagger module in ci/ with Flutter build/test logic
- Update .forgejo/workflows/ci.yml to use Dagger
- Move Android emulator tests to separate disabled workflow
- Add .daggerignore to exclude host junk

ci/.gitattributes

@@ -0,0 +1,4 @@
+/dagger.gen.go linguist-generated
+/internal/dagger/** linguist-generated
+/internal/querybuilder/** linguist-generated
+/internal/telemetry/** linguist-generated