Validate and normalize auto-postpone period to days (#2672)

* Validate and normalize auto-postpone period to days

- Add Entropy::AUTO_POSTPONE_PERIODS and validate auto_postpone_period against the allowed set
- Introduce auto_postpone_period_in_days for forms and entropy update endpoints
- Fall back to index 0 in knob partial when current value isn't in options
- Remove entropy_auto_close_options helper in favor of model constant
- Update tests to use allowed period values

* Use auto_postpone_period_in_days for JSON entropy updates

The JSON API was accepting auto_postpone_period (seconds) which
bypassed the days normalization and validation. Switch to
auto_postpone_period_in_days consistently and add explicit
wrap_parameters so flat JSON params are wrapped correctly for
the virtual attribute.

* Default to account or 30-day fallback when knob value is invalid

* Address PR review feedback for entropy validation

- Fall back to first knob option (index 0) when persisted value isn't in
  the allowed set, preventing nil index errors for legacy values
- Use integer division (1.day.to_i) for consistent day calculations

* Default to account entropy period instead of first option for knob fallback

* Test that default auto-postpone period is in the allowed periods

* Return 422 instead of 500 for invalid entropy auto-postpone values

Rescue ActiveRecord::RecordInvalid in entropy controllers so invalid
auto_postpone_period_in_days values return 422 Unprocessable Entity
instead of raising a 500.

* Fix NoMethodError when board entropy falls back to account default

Use container.account.entropy.auto_postpone_period_in_days instead of
container.account.auto_postpone_period_in_days since Account doesn't
delegate that method.

* Test board entropy fallback to account default for invalid periods

app/helpers/entropy_helper.rb

@@ -1,8 +1,4 @@
 module EntropyHelper
-  def entropy_auto_close_options
-    [ 3, 7, 30, 90, 365, 11 ]
-  end
-
   def entropy_bubble_options_for(card)
     {
       daysBeforeReminder: card.entropy.days_before_reminder,