Android birthday field does not retain `/` date separators when manually editing

[fluxbug-flutter]

Steps to reproduce

1. Start the Fluxer sign-up process on Android.
2. Open the birthday/date of birth modal.
3. Tap the pencil/edit option to manually edit the birthday.
4. Tap the birthday text field.
5. Delete a / from the date and try to enter it again.

Expected behaviour

The birthday field should retain the / date separators when editing, and it should be possible to enter them again if they are deleted, consistent with the birthday input behavior on other platforms.

Actual behaviour

On Android, the birthday field opens the numeric keyboard, which does not provide an option to type /. The / characters can also be removed with backspace, leaving no way to enter them again using the displayed keyboard.

Client and system settings

Version 2026.09.100, Beta 2, Channel Beta, Build 2527, Android 15 (arm64), Device samsung SM-G996U, Locale en-US, Push fcm, Flutter 3.47.5, Dart 3.13.4

Stances

Approvals

• CR: this field needs more restrictive inputs. Unexpected Keyboard can type slashes while in the number mode, but this field should also stop extra slashes from being added. Version 2026.09.100, Beta 2, Channel Beta, Build 2527, Android 16 (arm64), Device Google Pixel 9a, Locale en-US, Push fcm, Flutter 3.47.5, Dart 3.13.4
• Exactly what fullest said - Version 2026.09.100, Beta 3, Channel Beta, Build 77, iOS 26.6 (arm64), Device iPhone13,1, Locale en-GB, Push apns, Flutter 3.47.5, Dart 3.13.4

Denials

None

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Reported: #1718