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

signal_log.py

@@ -978,11 +978,6 @@ class SignalLogger:
             (now_iso, digest))
         return digest
 
-    def news_for(self, rowid: int) -> Tuple[Optional[str], Optional[str]]:
-        """(events_json, headlines_json) for a row, legacy or interned."""
-        with self._lock:
-            return read_news(self._conn, rowid)
-
     # ── advisory-event seeding / dedup ────────────────────────────
 
     def _seed_outcome(self, rowid: int, row: Dict[str, Any]) -> None: