Calibration metric (Brier-style) surfaced to world model

[CodeBuildder]

Context

Exposes per-action-type calibration scores via the world model Query API. Parent: #42.

Acceptance Criteria

• World model Query API includes GET /calibration returning per-action-type Brier scores
• Scores updated within one cycle of a new calibration record being written
• Calibration scores included in the Sentinel daily report data feed
• Score range 0.0–1.0 validated in unit tests (perfect vs worst case)

Dependencies

Blocked by: none | Blocks: none

Notes

No model tier.