fix: enforce OvidSubmitEnabled and handle 429 rate limits (closes #133, closes #134)

[negativeeddy]

Code Review Fix

Automated fix from deep-review investigation of #87.

Fixes #133
Fixes #134

Changes

Bug #1 — OvidSubmitEnabled enforcement (#133):

• Injected IOptions<ArmSettings> into OvidSubmitService
• Added early-return check in SubmitJobAsync when setting is false
• Added short-circuit in GetPendingJobsAsync to return empty list when disabled

Bug #2 — Rate limit handling (#134):

• Added explicit HTTP 429 handling in RegisterFingerprintAsync with Retry-After header logging
• Added explicit HTTP 429 handling in SubmitDiscAsync with Retry-After header logging
• Matches existing 429 handling in LookupByFingerprintAsync

Testing

• All 464 existing tests pass
• Build succeeds with 0 warnings, 0 errors