chore: dead-code + duplicate sweep; fix moon-flaky re-contact test

Dead code: removed an unused `settings` import (main.py), an unused
`RITUAL_HOLD_MS` import (RitualPanel), and an unused `beforeEach`
(SigilDesigner test). The `_refs` keep-alive in sdr.ts is deliberate
(holds hardware-pass constants) and stays; the orphaned .evp-scope /
.radio-waterfall CSS was already removed in an earlier lint pass.

Duplicate: coldSpot.ts and baseline.ts each carried the same time-aware
EMA alpha formula. Extracted it as baseline.emaAlpha(dtMs, tauMs) and
pointed both at it. coldSpot's pure-function core is deliberately NOT
merged into the stateful ThresholdBaseline class — different contract
(immutable-state-threaded vs internal-threshold), and forcing them
together would be an overhaul that risks the tested cold-spot logic.

Determinism fix: test_familiar_presence_answers_again_on_a_known_channel
pinned RETURN_CHANCE=1.0 but not the sky. Since the astronomy wiring made
the real return chance RETURN_CHANCE*(1 - veil_thinness*PULL), and
veil_thinness reads the *actual current moon phase*, a full-moon test run
dragged the effective chance to ~0.55 and the test failed ~45% of the
time. Now also pins VEIL_THINNESS_PULL=0 to isolate re-contact from the
veil influence (which has its own tests). Verified 12/12 consecutive
passes; it was ~7/12 before.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/RitualPanel.tsx

@@ -18,7 +18,6 @@ import type { CSSProperties } from 'react'
 import { useTranslation } from 'react-i18next'
 import { useSeance } from '../state/seance'
 import {
-  RITUAL_HOLD_MS,
   RITUAL_PROMPTS,
   holdProgress,
   nextStep,