Add EUR/USD support with modular per-pair signal producer pattern

- Register EUR/USD in config (pip 0.0001, EurUsdStrategyConfig)
- Create pair_signals/ module: registry + dispatcher with per-pair
  config factories (xauusd.py, eurusd.py) for easy add/remove
- EUR/USD gets forex-tuned regime weights, London+NY session hours,
  XAU strategy gates disabled
- Add defense-in-depth display_name guards in signal_aggregator
- Rename telegram_bot.py → testing_telegram_bot.py with separate
  bot token, both pairs with dedicated button rows
- Add EUR/USD to news engine affected pairs map
- 9 new tests (146 total, all passing)
- Zero changes to engine.py, data_provider.py, main.py, backtest/

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

signal_aggregator.py

@@ -417,6 +417,7 @@ class SignalAggregator:
             or (report.final_signal == SignalStrength.NEUTRAL and report.final_score < 0)
         )
         if (self.config.xau_strategy.enabled
+                and report.display_name == "XAU/USD"
                 and xau_is_sell_dir
                 and report.signal_quality not in self.config.xau_strategy.sell_min_quality):
             report.warnings.append(
@@ -426,7 +427,7 @@ class SignalAggregator:
             report.trade_setup = None
 
         # ── 7. Trade setup for actionable signals ──────────────────
-        if report.trade_setup is None and report.signal_quality in ("A+", "A"):
+        if report.trade_setup is None and report.signal_quality in ("A+", "A") and report.display_name == "XAU/USD":
             atr = (report.primary_analysis.key_levels.get("atr", 0)
                    if report.primary_analysis else 0)
             if atr > 0: