fix: surface unexpected repeat time-off failures

[Kevinjohn]

Summary

• Surface unexpected failures during repeat time-off requests while preserving validation feedback for invalid dates.
• Add regression coverage for repeat time-off error handling.

Validation

• pnpm run gate:all passed.
• pnpm run e2e passed (294 tests).

Merge predecessor: #1472

Closes #1467

Merge order

#1472 → #1473, #1474, #1466

• Set body text to 13px #1465 and chore: align repository configuration comments #1471 have merged. No textual conflicts with main (2950329) or between any pair of the remaining PRs. All four merged in this order onto main cleanly, and the combined tree passes format, typecheck, lint and the docs build (tree clean).
• Rewrite the documentation front door around four role quick starts #1466 lands last because it carries regenerated docs/ output.
• Each PR will be behind main once its predecessor lands; update the branch from main before merging.

Merge predecessor for this PR: #1472.

Conflicts: none.

[Kevinjohn]

Polish review: no P1 or P2 findings, no changes pushed.

• Comment-stripped AST comparison limits the behaviour change to useTimeOffRepeat.ts, repeatingTimeOff.ts, the regenerated primitive hashes in check-ui-primitives.mjs and two removed JSX comments in CommandPalette.tsx.
• Behaviour verified: a probe over 144 edge combinations (year 9999 and 0001 starts, end before start, every cadence, cutoffs at the start, end and policy maximum) produced only RepeatingDateError or a valid projection, so the preview's narrowed catch cannot crash the form on user input. The save path in timeOffFormSubmission.ts maps the new invalid-date code to the same date-domain message the old RangeError branch showed.
• node scripts/check-ui-primitives.mjs passes with the new hashes; the time-off, repeat, design-token, command palette, UI primitive and enlarged test files pass (17 files, 301 tests).
• Ladder passed on Node 24 at the PR head: pnpm run check:push (format, typecheck, lint with zero warnings, file-size policy) and pnpm run policy:comment-voice.
• Integration: chore: align repository configuration comments #1471, chore: align server, shared, and script comments #1472, fix: surface unexpected repeat time-off failures #1473, chore: clarify E2E test comments #1474 and Rewrite the documentation front door around four role quick starts #1466 merged in that order onto main at 8141c39 without conflicts; check:push, policy:comment-voice, docs:build (tree clean afterwards) and the documentation, runbook and user-story suites (430 tests) pass on the combined tree.

Merge predecessor: #1472.