Add Telegram bot and fix excessive API calls

- Add telegram_bot.py: full bot interface with /scan, /signals, /pair,
  /all, /tf, /watch, /unwatch, /status, /help commands; per-chat state;
  background thread pool for analysis; auto message splitting
- Fix data_provider: warn once per symbol with no API data and cache
  synthetic fallback to prevent redundant individual API calls
- Fix signal_aggregator: derive spread estimate from already-fetched
  primary DataFrame instead of making a separate M5 API call per pair
- Add python-telegram-bot[job-queue]>=20.0 to requirements.txt

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

signal_aggregator.py

@@ -202,7 +202,11 @@ class SignalAggregator:
         report.news_description = sent_desc
 
         # ── 5. Spread Estimate ─────────────────────────────────────
-        report.spread_estimate = self.data_provider.get_spread_estimate(symbol)
+        # Derive spread from already-fetched primary_df to avoid a separate M5 API call
+        if primary_df is not None and not primary_df.empty:
+            report.spread_estimate = float((primary_df["High"] - primary_df["Low"]).median())
+        else:
+            report.spread_estimate = self.data_provider.get_spread_estimate(symbol)
 
         # ── 6. Compute Final Signal ────────────────────────────────
         self._compute_final_signal(report)