calibration: config-drift section in the maintainer recap

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Problem

Epic #8211 track A. Drift alerts are point-in-time; the weekly maintainer recap (src/services/maintainer-recap.ts + maintainer-recap-calibration.ts) is where a standing drift should be impossible to miss. Today the recap's calibration section knows nothing about drift.

Requirements

⚠️ Required pattern. Mirror buildCalibrationRecapSection (src/services/maintainer-recap-calibration.ts) exactly: a pure section builder over a plain source struct, wired into the recap assembly the same way, with the same public-safe boundary (aggregate numbers + knob ids only — never corpus content).

• Pure section builder: given each live knob's current drift report (the shape the sentinel already computes), render: clean knobs as one summary line; each drifting knob with direction, live vs dominating value, corpus sizes, and how long the episode has stood (from the sentinel's fingerprint timestamp).
• Explicit empty-state line when the sentinel flag is off ('drift sentinel disabled') — absence of data must be distinguishable from absence of drift.
• Wire into the recap assembly behind the existing recap plumbing; no new scheduling.

Deliverables

• Pure section builder with 100% line+branch coverage (drifting/clean/disabled/mixed states, invariant test that no corpus content appears)
• Recap assembly wiring + snapshot-style test update

Links & Resources

#8211 (epic), the sentinel sub-issue (blocked-by), src/services/maintainer-recap-calibration.ts

Boundaries

Read-and-render only. Do not modify the sentinel or the knobs endpoint.

[linear-code]

JSO-5698