chore: drop unused imports and a dead constant (no behaviour change)

- backtest/diagnose_filters: unused BacktestConfig import
- pair_signals/__init__: unused PlatformConfig import
- scripts/shadow_scan: unused pandas import
- research burst_precursors / calendar_impact / duka_spread: unused sys / COST / struct
- test_all: MagicMock, StringIO, Colors and two function-local imports that
  nothing in the test bodies used
- telegram_bot: ViolentWatch is only a type hint -> imported under TYPE_CHECKING

compare_oanda_tiingo.py and oanda_td_divergence.py are left alone here because
the hygiene commit deletes them.

Suite: 464 passed, 0 failed (unchanged).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0156YhogLytzj9P2iH1skGbL

telegram_bot.py

@@ -50,7 +50,7 @@ import threading
 import time
 from concurrent.futures import ThreadPoolExecutor
 from datetime import datetime, timezone
-from typing import Any, Dict, List, Optional, Set
+from typing import TYPE_CHECKING, Any, Dict, List, Optional, Set
 
 from telegram import InlineKeyboardButton, InlineKeyboardMarkup, Update
 from telegram.constants import ParseMode
@@ -77,7 +77,10 @@ from market_outlook import maybe_run_outlook
 from news_engine import FundamentalContext, NewsEngine
 from pair_signals import PAIR_PRODUCERS
 from signal_aggregator import SignalAggregator, SignalReport
-from violent_watch import ViolentWatch, attach_watch, should_send_headsup
+from violent_watch import attach_watch, should_send_headsup
+
+if TYPE_CHECKING:  # type hints only — ViolentWatch is never needed at runtime here
+    from violent_watch import ViolentWatch
 
 _APP = get_app_config()