fix: render validation state on DateTimeControl and ColorPicker

[dakorpar]

Closes #113

Problem

DateTimeControl (backing addDate(), addDateTime(), addTime()) uses StandardValidationTrait, which supplies showValidation() — but the class never declared implements IValidationInput. BootstrapRenderer::renderControl() gates that call on the interface:

if (($this->form->showValidation || $control->hasErrors()) && $control instanceof IValidationInput) {
    $controlHtml = $control->showValidation($controlHtml);
}

so the input never received is-invalid.

The <div class="invalid-feedback"> was in fact emitted all along. Bootstrap styles .invalid-feedback as display: none unless a sibling input carries .is-invalid, which is why the message rendered but stayed invisible — matching the screenshot in the issue.

-<input type="date" name="date" id="frm-date" class="form-control">
+<input type="date" name="date" id="frm-date" class="form-control is-invalid">
   <div class="invalid-feedback">Foobar error message<br></div>

Fix

Added implements IValidationInput to DateTimeControl. ColorPicker had the identical trait/interface mismatch — found by auditing every class in src/Inputs/ — and is fixed the same way. Those two were the only ones; DateInput/DateTimeInput inherit the interface via TextInput.

No renderer changes. No tests/data/ fixtures shifted — none exercise an errored date or color field.

Verified

• addDate / addDateTime / addTime / addColor, each with an error → is-invalid plus a visible feedback div
• $form->showValidation = true with no errors → is-valid, consistent with TextInput
• Bootstrap 4 and Bootstrap 5 output
• Inside a BootstrapRow / BootstrapCell grid cell
• Standalone getControl() without the renderer → unchanged

make tests (150 tests), make phpstan (level 7), make cs all green. Regression tests added to DateTimeControlTest and ColorPickerTest.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.94%. Comparing base (303f8eb) to head (66fda61).

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #127   +/-   ##
=========================================
  Coverage     96.94%   96.94%           
  Complexity      308      308           
=========================================
  Files            25       25           
  Lines           983      983           
=========================================
  Hits            953      953           
  Misses           30       30           

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