Remove synthetic data fallback; fix concurrent API credit exhaustion

data_provider:
- Remove _generate_synthetic_data entirely — no more fake prices
- Raise DataUnavailableError instead of falling back to synthetic data
  (no API key, daily limit hit, API returns no values, fetch failure)
- Move rate limiter to module-level globals (_rate_lock, _rate_request_times,
  _rate_daily_credits) so all ForexDataProvider instances running in parallel
  threads share the same 8-credit/min and 800-credit/day accounting
- _throttle now raises DataUnavailableError on daily limit (was silent return False)
- Remove _no_api_data tracking, numpy/hashlib imports

telegram_bot:
- Detect F-grade reports caused by data unavailability and show clean
  "Data unavailable" line per TF instead of a garbled zero-price card

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

telegram_bot.py

@@ -137,6 +137,19 @@ def _build_combined_signal(
             continue
         r = reports[0]
 
+        # If primary TF data was unavailable the engine returns grade F with a warning.
+        # Show a clean "data unavailable" line instead of a garbled card.
+        if r.signal_quality == "F" and any(
+            "unavailable" in w.lower() or "api" in w.lower() or "credits" in w.lower()
+            for w in r.warnings
+        ):
+            lines.append("")
+            lines.append("────────────────────────")
+            lines.append(f"<b>{tf}</b> — ❌ Data unavailable")
+            if r.warnings:
+                lines.append(f"<i>{_h(r.warnings[0])}</i>")
+            continue
+
         dot    = _grade_dot(r.signal_quality)
         action = _signal_action(r.final_signal)