feat(routes-f): add relative-date parser endpoint (#880)

[utahkanz-ops]

Summary

Closes #880

Parses natural relative date expressions into absolute ISO 8601 timestamps.

Endpoint

POST /api/routes-f/relative-date

Request:

{ "text": "tomorrow", "now": "2026-05-28T12:00:00.000Z" }

Response (200):

{ "resolved": "2026-05-29T12:00:00.000Z", "matched": "tomorrow" }

Error (400): returned for unparseable input or invalid now value.

Supported Phrases

Phrase	Behavior
tomorrow	baseDate + 1 day
yesterday	baseDate − 1 day
next monday	Next calendar Monday
in N days	baseDate + N days
in N weeks	baseDate + N×7 days
N days ago	baseDate − N days
N weeks ago	baseDate − N×7 days

Files Changed

All files scoped exclusively to app/api/routes-f/ — no modifications outside this directory.

• app/api/routes-f/relative-date/route.ts — route handler
• app/api/routes-f/__tests__/relative-date.test.ts — 9 Jest unit tests

Test Results

PASS app/api/routes-f/__tests__/relative-date.test.ts
  ✓ parses tomorrow relative to now
  ✓ parses yesterday relative to now
  ✓ parses next monday relative to now (which is a Thursday)
  ✓ parses in 3 days relative to now
  ✓ parses 2 weeks ago relative to now
  ✓ rejects unparseable input with 400
  ✓ rejects invalid now ISO string with 400
  ✓ rejects non-string text with 400
  ✓ uses the current system time if now is not provided

Tests: 9 passed, 9 total

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