feat: replace quota input with amount-first UI and atomic quota adjustment

- Refactor token, redemption, and user quota inputs to prioritize monetary
  amount entry, with raw quota input collapsed by default
- Add atomic quota adjustment modal for users with add/subtract/override modes,
  bypassing batch update queue for immediate DB consistency
- Make user quota fields readonly in edit form; all modifications go through
  the dedicated adjust-quota modal via POST /api/user/manage
- Add DecreaseUserQuota `db` parameter for direct DB writes, matching
  IncreaseUserQuota behavior
- Support negative quota display in amount conversion helpers
- Add i18n keys for all new UI strings across all locales

.gitignore

@@ -29,3 +29,5 @@ data/
 .gomodcache/
 .gocache-temp
 .gopath
+
+token_estimator_test.go