Add per-session bay calibration as a read-time layer

[chayuto]

Why

A session recorded in a bay whose target line is misaimed reads every direction metric wrong by a constant: face angle, club path, and launch direction shift together while face-to-path stays put (it is a difference of two directions, so the offset cancels). The 2026-08-01 SIM bay session read 2.8 degrees left of the range bay baseline this way.

What

Stored telemetry stays exactly as TrackMan reported it. The correction is a calculation layer applied at read time, scoped per session.

• training_sessions.calibration_offset_deg (float, nullable, -15..15). Degrees added to bay-reported direction metrics. Positive when the bay read left of true.
• PATCH /api/v1/sessions/:id sets or clears the offset. Requires telemetry:write, audited via paper_trail, and it is the only mutable session field.
• GET /api/v1/stats/clubs?calibrated=1 returns corrected aggregates, computed in SQL: face and path get the offset added, lateral carry spread rotates by it. face_to_path is never corrected.
• Dashboard: a Bay cal. toggle in the filter bar corrects charts client-side (pure math, no shot refetch; only club aggregates refetch). Selecting a session reveals an offset editor.
• Ball trajectories stay raw; at chart scale the side error is within line width.

Tests

• Request specs: offset update (happy path, clear, validation, scope, cross-user, audit attribution, telemetry-fact immutability), calibrated vs raw stats (offset applied, f2p and SD invariant, no-offset no-op).
• Full local CI: rspec (86 examples), rubocop, brakeman, bundler-audit, web lint and build all green.