feat(ci): check-test-suite-ceilings grades each package's suite against its ceiling

Reads the per-shard timing captures, sums a file-sliced package's parts
across shards, and grades every executed package against the generated
ceiling in scripts/test-shard-timings.json: over its ceiling, or absent
from the dataset, is red, naming the package and its slowest test files;
a provisional or carried package prints why it has no ceiling and is not
red; a dataset without the `ceilings` field reads NOT MEASURED. A ceiling
rises only by a RULED_CEILING_RAISES entry naming the ruling comment.

Claude-Session: https://claude.ai/code/session_0115N1oNnQS5WqofZ2DzaT3q
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude