Backfill complete series for DCC, Primal Hunter, DOTF, HWFWM, Path of Ascension

Manual backfill of 57 missing audiobooks across 5 major series.
Audible API rate-limits with 200 OK + empty products (not 429),
making automated backfill unreliable after bulk fetches.

Added manual-backfill.ts for direct DB insertion when API is unavailable.
Added CLAUDE.md documenting Audible API quirks and workarounds.