## Problem
Some users reported they couldn't register: they filled the form
correctly, pressed the button, saw a loading spinner, then got bounced
back to the registration page with **no error message**. Meanwhile 20-30
users register fine every day, and the issue wasn't reproducible by the
team.
## Root cause
The register form sends a **hidden, browser-auto-detected `timezone`**
field (`Intl.DateTimeFormat().resolvedOptions().timeZone`). The backend
validated it with Laravel's `timezone` rule:
```php
'timezone' => ['nullable', 'string', 'timezone'],
```
That rule rejects **legacy IANA aliases** that many browsers/OSes still
emit — e.g. `Asia/Calcutta`, `Asia/Saigon`, `Asia/Rangoon`,
`US/Pacific`. Proof on PHP 8.4:
```
in_array("Asia/Calcutta", DateTimeZone::listIdentifiers()) → false
```
When validation failed, Fortify redirected back with a `timezone` error
— but the form had **no error display** for timezone (every other field
has one). Result: spinner → silent bounce → no message → and the user
can't fix a hidden field anyway. The team couldn't reproduce because
their browsers send canonical zones that pass. Production tzdata may
reject even more zones.
## Fix
- Stop validating the auto-detected hidden field against the strict
timezone list.
- Add `normalizeTimezone()`: keep recognized zones (including BC aliases
via `DateTimeZone::ALL_WITH_BC`), drop anything unrecognized to `null`.
Registration can never be blocked by it again.
- Surface `errors.timezone` in the form as a safety net so a
hidden-field failure can never be silent in the future.
## Tests
- Legacy alias `Asia/Calcutta` → registers, stored as-is.
- Unrecognized zone → registers, stored `null`.
- All existing registration tests pass (13 passed).
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