fix: Missing circuit breaker checks in several provider functions

[deucebucket]

Bug

Several provider functions call rate_limit_wait() but skip the is_circuit_open() check, wasting work when a provider is known-broken:

1. identify_book_from_transcript() (openrouter.py ~line 223) — waits 5s then calls a circuit-broken provider
2. detect_audio_language() (gemini.py ~line 336) — extracts audio sample + base64 encodes before discovering Gemini is circuit-broken
3. lookup_audnexus_by_asin() (audnexus.py ~line 153) — calls record_api_success() BEFORE checking the HTTP status code, incorrectly resetting the circuit breaker on 500s

Fix

1. Add if is_circuit_open('openrouter'): return None at the top of identify_book_from_transcript()
2. Add if is_circuit_open('gemini'): return None before the audio extraction in detect_audio_language()
3. Move record_api_success('audnexus') after the response.status_code == 200 check in lookup_audnexus_by_asin()

Severity

Low — not a spam risk (rate limiters still apply) but wastes CPU/disk on audio extraction and makes circuit breakers less effective.

Found via code audit.

[deucebucket]

Implemented on main by commit 2e0a701: provider circuit-breaker checks now occur before expensive work, and Audnexus records success only after a successful response.