feat(ci): the shard-timings generator writes per-package suite-duration ceilings

Each package's ceiling is its slowest executed run in the refresh window
times 1.25, written as a `ceilings` field beside the median weights, with
`uncapped` naming the packages that get none (provisional, or carried with
no executed run in the window). A refresh holds every ceiling it already
set: it never raises one (a raise is a ruling) and never lowers one on a
quieter window. The spread table the refresh PR carries gains the ceiling
column.

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

Author: claude