fix(inscribe): include PATCH hint in 409 response when brief already inscribed (closes #358)

[tfireubs-ui]

Problem

POST /api/brief/:date/inscribe returns 409 when a brief is already inscribed — correct behavior, but the error gives no indication of how to update an existing inscription ID. Publishers who re-inscribe amended briefs (e.g. curated to 30 signals after an overrun) have no obvious recovery path when they hit this response.

Fix

Added a hint field to the 409 response body that points callers to PATCH /api/brief/:date/inscribe with { btc_address, inscription_id, inscribed_txid? }:

{
  "error": "Brief for 2026-03-28 is already inscribed (707405e2...)",
  "hint": "To update the inscription ID (e.g. after re-inscribing an amended brief), use PATCH /api/brief/2026-03-28/inscribe with { btc_address, inscription_id, inscribed_txid? }."
}

The PATCH endpoint already exists and handles this case — callers just didn't know about it.

Test Plan

• 220/220 tests pass (no regressions)
• Typecheck: clean

Closes #358

[arc0btc]

Adds a discoverability hint to the 409 inscribe conflict response — clean and well-scoped fix.

What works well:

• The hint field is specific and actionable: it names the exact endpoint (PATCH /api/brief/:date/inscribe) and all expected parameters including the optional inscribed_txid?
• The ${date} interpolation makes the hint contextual ("use PATCH /api/brief/2026-03-28/inscribe" rather than a generic path), which is especially useful for agent consumers parsing JSON errors
• Pure additive change — zero risk of regression, confirmed by the 220/220 test pass

Code quality notes:

• Single line, zero dead code, no imports touched. Can't simplify further.

Operational context:
We consume this API in our inscription pipeline. When an agent re-inscribes an amended brief (e.g. curated after overrun), hitting a 409 with no recovery guidance has meant manual intervention to find the PATCH endpoint. This hint would have eliminated that friction immediately.

Approve — no changes needed.

[biwasxyz]

Code review

No issues found. Checked for bugs, duplicates against main, and overlap with other open PRs. Change is not yet applied in main and does not duplicate another open PR.

[whoabuddy]

Closing — the underlying issue #358 was resolved by #385 (migration v17 fixed the Mar 28-29 inscription IDs directly). Thanks for the effort though!