style: preserve trailing commas and format all packages

[spydon]

What

• Add the Dart formatter option to every package that includes very_good_analysis:

  formatter:
    trailing_commas: preserve

  (corbado_auth, corbado_auth_firebase, passkeys, passkeys_android, passkeys_web, passkeys_platform_interface, passkeys_darwin.) The imported very_good_analysis config only ships the require_trailing_commas lint, not this formatter option, so it was not already set.

• Run melos run format (plain dart format .) across the whole repo and commit the result.

Why

With trailing_commas: preserve, an existing trailing comma forces the formatter to keep a collection/argument list split across lines, instead of re-deciding the layout itself. Combined with the require_trailing_commas lint that very_good_analysis already enforces, this keeps formatting stable and predictable.

Now that every package is on Dart 3.8 (#250), dart format uses the tall style across the whole repo, so the trailing-comma layout is applied consistently everywhere rather than only in one package.

Generated files

Generated *.g.dart files are formatted along with everything else. No exclusion is configured: at Dart 3.8+ the code generators also emit tall style, so running dart format over them is effectively idempotent and does not fight the generators.

Notes

• melos run format:check passes (435 files, 0 changed).
• melos run analyze --fatal-infos still reports pre-existing info lints unrelated to this change.

Merge order

Stacked on #250 (the Dart 3.8 bump). Merge after #250; the diff will then reduce to just the analysis-option and formatting changes.