REQ-011 asks for both required-field errors via per-field aria-invalid, but the
blank-date error was rendered as a standalone <p> after the date card while the
date input's aria-invalid only reflected the client-side malformed-date cue.
DatePrecisionField gains a `dateError` prop: a server error now marks the field
aria-invalid and renders inline under the input (sharing the same error id), and
EventForm drops its detached <p>. While here, migrate the field's two error
texts from hard-coded text-red-600 to the semantic `text-danger` token so they
keep ≥4.5:1 contrast in dark mode (the token remaps; #dc2626 was borderline) —
this also fixes the contrast for WhoWhenSection, the other consumer.
Component test asserts the date input gains aria-invalid on a server date error.
Addresses PR #832 review (Requirements Engineer REQ-011; UI/UX dark-mode contrast).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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