Replace px-0 py-0 override with px-3 py-1 so placeholder text is
never flush against the edge. The ::placeholder pseudo-element
inherits box padding from the textarea; zeroing it out removed all
visual breathing room for the hint text.
Also adds tests/textarea.test.ts that locks down this behaviour via
class-string assertions on the resolved cn() output.
- add normalizeAiDateString() to coerce bare ISO datetimes, date-only
strings, and fractional-second variants into offset-aware format
- apply via z.preprocess in AiEventResponseItemSchema so Zod validation
no longer rejects AI responses missing a timezone offset
- fix system prompt to use toISOString() (unambiguous UTC) and clarify
expected datetime format for the AI model
- install bun-types and add to tsconfig so bun:test resolves cleanly
- add 8 behaviour-driven tests covering all normalizer edge cases
