tri priority --check: anomalies in priority labels; no loop tool may shadow a stdlib module #6378

Problem

1. Labels can be wrong in ways tri priority shows but does not flag: more criticals than CRITICAL_CAP (the extras quietly run as HIGH), an issue with labels of two levels, or a labelled issue with an open blocker.
2. PR feat(queen): the Queen's priority, decided in t27, and tri priority (Closes #6366) #6367 first named its tool scripts/tri_loop/queue.py. Every tool run from scripts/tri_loop then imported it instead of the stdlib queue, and tri stranded broke in CI. Nothing stops the next tool name from doing the same.

Goal

• tri priority --check prints each anomaly and exits 1 when there is one (still read-only).
• loop-tools-gate fails when a file in scripts/tri_loop has the name of a stdlib module (sys.stdlib_module_names).

Acceptance

• Fixtures cover each anomaly kind, with a clean listing as the negative control.
• The guard catches a planted queue.py.

Refs #6366