Obsolete Crowdin strings are never removed

`crowdin-tx.yml` runs `upload_sources: true` with no obsolete-string handling, and `crowdin.yml` sets only `preserve_hierarchy`. The Crowdin CLI does not remove strings that have disappeared from the source file unless `--delete-obsolete` is passed, so every key ever deleted from `translations/app_en.arb` is still in the project.

Cost compounds quietly:

- Translators spend effort on strings the app no longer has.
- Completion percentages are measured against a denominator that includes dead keys, so "100%" stops meaning the app is fully translated.
- `crowdin_summary.py` reports those same inflated numbers into the PR body and the job summary.

ChameleonUltraGUI handles this explicitly: `updateCrowdin.py` diffs `app_en.arb` against `main~1` and issues deletes through the strings API for keys that vanished.

- [ ] Confirm the input `crowdin/github-action@v2` exposes for `--delete-obsolete` (the CLI flag on `crowdin upload sources`)
- [ ] Enable it, or add a scheduled reconciliation that reports orphans without deleting
- [ ] Audit how many orphans exist today before turning deletion on — it is destructive, and a bad `.arb` in history could have registered keys worth keeping

Prefer a report-only first pass. Deleting a string in Crowdin discards its translations across every locale.