[Formplayer] adate: year input broken, unknown checkbox doesn't persist

[arthur-d42]

Component

• formulus (React Native mobile app)
• formulus-formplayer (React web app)
• synkronus (Go backend server)
• synkronus-cli (Command-line utility)
• Documentation
• Other (please specify)

Description

The adate (approximate date) question type has three bugs that make it unusable: year selection is impossible, toggling "Unknown" after entering a value doesn't persist, and navigating away then back throws an error.

Details

• Year input impossible: Always occurs. The handleYearChange regex /^\d{4}$/ rejects any partial input ("2", "20", "202"), so a year can never be typed.
• "Unknown" checkbox doesn't write ??: Occurs when checking "Unknown" after a value is already entered (only way to enter a valid date is by pressing "today" to get year filled).

Steps to Reproduce

1. Open a form with an adate question
2. Try to type a year: nothing is accepted
3. Select a month, then check the "Unknown" checkbox for that month: the stored value does not change to ??

Expected Behavior

• User can select a year
• Checking "Unknown" after entering a value stores ?? in the date component

Actual Behavior

• Year field rejects all input
• "Unknown" checkbox has no effect on stored data when toggled after a value is entered

Environment

Component version/branch: dev branch

Additional Context

Root cause for all three bugs is the updateFormData useCallback pattern - it captures stale state when called synchronously after setState. Fix is replacing it with a reactive useEffect that syncs to the form on state change, plus refs to prevent circular updates between the init and sync effects.
In my opinion dropdowns would be a better fit here since day, month, and year are all fixed lists of options. That also removes the year typing problem entirely.