When admin registers a materialized BQ row with bucket+source_table but
no source_query, the server generates 'SELECT * FROM `<project>.<ds>.<tbl>`'
from instance.yaml's configured BQ project. Same fallback fires on PUT
when flipping to materialized. The backtick rejection guard, which was
appropriate for DuckDB-flavor source_query, is relaxed for materialized
rows since the new wrapping path (Task 2) runs admin SQL through BQ
jobs API which uses BQ-native syntax (backticks for dashed identifiers).
