chore: remove test-only helpers and the duplicate confirmation map (no behaviour change)

- telegram_bot._format_scan_summary: multi-pair "auto-scan summary" leftover;
  production sends per-report format_signal_message. Its only caller was a test.
- telegram_bot.scan_keyboard: thin wrapper only a test called; main_menu_keyboard
  already builds from _scan_button_rows directly.
- telegram_bot.AUTOSCAN_CONFIRMATIONS was byte-identical to TF_CONFIRMATIONS;
  the candle loop now reads the one map (app_config comment updated).
- SignalLogger.news_for: one-line wrapper over the module-level read_news that
  every real reader uses; the test now calls read_news like its neighbours.
- pair_signals.get_supported_pairs: PAIR_PRODUCERS is the registry; the test
  lists it directly.

Suite: 461 passed, 0 failed (two helper-only tests removed).

Claude-Session: https://claude.ai/code/session_0156YhogLytzj9P2iH1skGbL

app_config.py

@@ -82,7 +82,7 @@ load_dotenv()
 _VALID_QUALITIES = ("A+", "A", "B", "C")
 _VALID_LOG_LEVELS = ("DEBUG", "INFO", "WARNING", "ERROR", "CRITICAL")
 # Timeframes the bot's candle-boundary scheduler supports (must have
-# AUTOSCAN_CONFIRMATIONS entries in telegram_bot.py).
+# TF_CONFIRMATIONS entries in telegram_bot.py).
 _SCANNABLE_TFS = ("M5", "M15", "H1", "H4")
 
 _KNOWN_TOP = {"telegram", "data_providers", "scanning", "pairs", "log_level",