feat(routes-f): roman numeral converter (1 to 3999)

[davedumto]

Summary

Add a Roman numeral converter at app/api/routes-f/roman/route.ts. Convert numbers to Roman numerals and vice versa (1–3999).

⚠️ Scope Constraint — READ BEFORE STARTING

All files for this task must live inside app/api/routes-f/. This includes:

• The route handler (e.g. app/api/routes-f/<feature>/route.ts)
• Any helpers/utilities (e.g. app/api/routes-f/<feature>/_lib/helpers.ts)
• Any types (e.g. app/api/routes-f/<feature>/_lib/types.ts)
• Any tests (e.g. app/api/routes-f/<feature>/__tests__/route.test.ts)

Do not modify, import from, or add files to lib/, utils/, types/, components/, or anywhere else outside app/api/routes-f/. If you need shared logic, duplicate it inside your subfolder. Keeping everything scoped to this folder is intentional — it keeps these tasks independent and mergeable in any order.

Requirements

• GET /api/routes-f/roman?to_roman=1994 returns { roman: "MCMXCIV" }
• GET /api/routes-f/roman?to_number=MCMXCIV returns { number: 1994 }
• Valid range: 1–3999
• Must use subtractive notation (IV not IIII, IX not VIIII)
• Reject invalid Roman input (e.g., IIII, VV, IC) with 400
• Reject out-of-range numbers with 400
• Include unit tests covering boundary values and invalid inputs

Acceptance Criteria

• Round-trip (number -> roman -> number) is lossless for 1–3999
• Subtractive notation strictly enforced
• Invalid inputs rejected
• Tests cover boundaries (1, 3999) and known tricky cases (4, 9, 40, 90, 400, 900)
• All files inside app/api/routes-f/roman/