Adds Pass 3 to `_bq_guardrail_inputs` that scans user SQL for full
backtick paths `<project>.<dataset>.<table>` and gates them
identically to the `bq."<dataset>"."<table>"` pass:
- Project must match the configured BigQuery data project
(`get_bq_access().projects.data`). Mismatch → HTTP 403
`bq_path_cross_project`.
- Path must point at a registered row. Unregistered → HTTP 403
`bq_path_not_registered`.
- Non-admin caller must hold a grant on the registered row's id.
Missing grant → HTTP 403 `bq_path_access_denied`.
Pre-fix, full backtick paths bypassed Agnes RBAC entirely — only the
service account scope limited reach. Post-fix the boundary matches
what `agnes catalog`-driven flows already enforce. Admin still
bypasses the per-id grant check but cannot bypass registration or
project match.
Pass 3 also seeds `dry_run_set` for resolved registered paths so the
cost-cap dry-run runs against the same physical table the user named
— composing cleanly with the Layer 2 fail-fast fallback.
824e3cb636