fix: Missing rate limiting on BookDB contribute/consensus functions

[deucebucket]

Bug

Two BookDB/Skaldleita API functions lack rate limiting:

1. contribute_to_bookdb() (bookdb.py ~line 488) — POSTs to Skaldleita without calling rate_limit_wait('bookdb'). Checks circuit breaker but has no per-call pacing.
2. lookup_community_consensus() (bookdb.py ~line 568) — GETs from Skaldleita with NO rate limiting AND no circuit breaker check.

While these are called per-book (not in tight loops), they bypass the 3.6s bookdb pacing that all other BookDB functions respect.

Fix

Add rate_limit_wait('bookdb') to both functions. Add is_circuit_open('bookdb') check to lookup_community_consensus().

Severity

Medium — indirect protection from pipeline batch delays, but direct protection is missing.

Found via code audit.