Switch data source to Finnhub API; remove synthetic data fallback

Adds FinnhubDataProvider as a drop-in replacement for ForexDataProvider.
Rate limit or API errors raise DataUnavailableError immediately — the
Telegram bot shows a clean per-TF error card rather than fake prices.

- data_provider_finnhub.py: Finnhub client, OANDA symbol mapping,
  4h resampled from 60-min candles, shared module-level rate limiter
  (60 calls/min free tier), full OHLCV validation copied from original
- signal_aggregator.py: import FinnhubDataProvider alias ForexDataProvider
- config.py: add finnhub_api_key field (FINNHUB_API_KEY env var overrides)
- telegram_bot.py: remove synthetic-data warning and _SUPPORTED_PAIRS;
  unsupported pairs now show the engine's "data unavailable" card
- requirements.txt: add finnhub-python>=1.0

Set FINNHUB_API_KEY env var before running. main branch is untouched.

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

telegram_bot.py

@@ -30,7 +30,7 @@ from telegram.constants import ParseMode
 from telegram.ext import Application, CommandHandler, ContextTypes
 
 from config import (
-    MAJOR_PAIRS, CROSS_PAIRS, SYMBOL_DISPLAY,
+    MAJOR_PAIRS, SYMBOL_DISPLAY,
     PlatformConfig, SignalStrength, Timeframe,
 )
 from signal_aggregator import SignalAggregator, SignalReport
@@ -54,8 +54,7 @@ _TF_CONFIRMATIONS = {
     "D1":  [Timeframe.H4,  Timeframe.W1],
 }
 
-_SUPPORTED_PAIRS = set(MAJOR_PAIRS + CROSS_PAIRS)
-_GRADE_RANK      = {"A+": 0, "A": 1, "B": 2, "C": 3, "D": 4, "F": 5}
+_GRADE_RANK = {"A+": 0, "A": 1, "B": 2, "C": 3, "D": 4, "F": 5}
 _EST             = ZoneInfo("America/New_York")
 
 # ── Formatting helpers ──────────────────────────────────────────────
@@ -114,7 +113,6 @@ def _build_combined_signal(
     results_by_tf: Dict[str, List[SignalReport]],
     display: str,
     now_str: str,
-    synthetic: bool = False,
 ) -> str:
     """
     Single message showing all timeframes stacked.
@@ -125,11 +123,7 @@ def _build_combined_signal(
     lines.append(f"🌐 <b>{_h(display)} — Signal Analysis</b>")
     lines.append(f"🕐 {now_str}")
 
-    if synthetic:
-        lines.append(
-            "⚠️ <b>Note:</b> Not on Twelve Data free tier — "
-            "prices are <b>simulated</b> data."
-        )
+    # Finnhub branch: no synthetic data — real prices or error shown per-TF.
 
     for tf in SCAN_TIMEFRAMES:
         reports = results_by_tf.get(tf, [])
@@ -360,9 +354,8 @@ class ForexTelegramBot:
         raw = args[0].upper().replace("/", "").replace("_", "")
         if not raw.endswith("=X"):
             raw += "=X"
-        display  = SYMBOL_DISPLAY.get(raw, raw.replace("=X", ""))
-        tfs_str  = " · ".join(SCAN_TIMEFRAMES)
-        synthetic = raw not in _SUPPORTED_PAIRS
+        display = SYMBOL_DISPLAY.get(raw, raw.replace("=X", ""))
+        tfs_str = " · ".join(SCAN_TIMEFRAMES)
 
         msg = await update.message.reply_text(
             f"🔄 Analyzing {_h(display)} across {_h(tfs_str)}…"
@@ -376,7 +369,7 @@ class ForexTelegramBot:
                 await msg.edit_text(f"❌ No data returned for {_h(display)}")
                 return
 
-            text = _build_combined_signal(results_by_tf, display, now_str, synthetic)
+            text = _build_combined_signal(results_by_tf, display, now_str)
             await msg.delete()
             await self._send_html(update, text)