Redesign tack detection: time-based windows + circularMAD stability

Replace the point-count window (HALF_WIN=2) with 30s time-based settle
windows that give consistent reliability regardless of GPS update rate
(1 Hz FULL vs 0.2 Hz ECONOMY). Key changes:

- Before/after windows are time-based (T_SETTLE=30s) around a guard
  zone (T_MANEUVER=30s), not point counts.
- Stability uses circularMAD (<20°) across all fixes in each window,
  replacing the single-pair spread check. This correctly handles
  0°/360° wrap and suppresses random anchor-watch COG noise (MAD≈90°).
- No SOG gate: averaging 30 fixes over 30s reduces noise by √30
  regardless of boat speed. A boat at anchor has MAD≈90° and is
  rejected by the stability check.
- MAX_DELTA raised to 160° (covers deep jibes the old 140° missed).
- START_SKIP reduced to 60s (stability check handles cold-start noise).
- De-duplication uses adjacent-candidate comparison so a long stream
  of raw candidates from one maneuver stays in a single group even if
  it spans >MIN_GAP_MS in total.
- Position refined to max instantaneous heading rate within the
  maneuver zone.
- Mode: CRUISING (conservative). Race mode noted as future backlog.

16/16 unit tests pass at 1 Hz (FULL mode GPS rate).

https://claude.ai/code/session_01YUbuZNDAoLea4cf9UGQ9qn

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