chore(pricing): capture Apple's real 409 code on pricing schedule create

Summary

47 of 170 installs hit 409 on asc pricing schedule create (5.x, 14 days), and #2606 showed the rate is independent of --start-date. POST /v1/appPriceSchedules is the only write verb (no PATCH/DELETE) and replaces the app's single schedule, so it is not an existence conflict and --if-exists does not map.

What to do

Capture Apple's real 409 body for this endpoint (the disposable app 6759231657 is authorized for live mutations of this kind if needed; record what was run), then map the code/detail to a specific, actionable error message (e.g. a schedule change already pending, base territory mismatch, price point not available in a territory) and classify it correctly for telemetry.

Acceptance criteria

• the real 409 body checked in as a fixture
• specific message per identified cause; other 409s unchanged