fix(universe): robust iShares→yfinance ticker mapping for class shares

- Filter to Asset Class == Equity only (removes UBFUT, XTSLA non-equity rows)
- Static remap for 16 known iShares compact tickers → canonical yfinance hyphenated form
  (BRKB→BRK-B, BFA→BF-A, HEIA→HEI-A, LENB→LEN-B, UHALB→UHAL-B, CWENA→CWEN-A, etc.)
- Avoids false positives: META, NVDA, TSLA, ABNB, ZBRA, CMCSA preserved correctly
- Fix C401 in ohlcv_cache.py (set comprehension)
- Result: 1003 clean equity tickers from Russell 1000

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

tradingagents/dataflows/data_cache/ohlcv_cache.py

@@ -51,7 +51,7 @@ PERIOD_TO_DAYS: Dict[str, Optional[int]] = {
 
 def _cache_key(tickers: List[str]) -> str:
     """Stable 12-char hash of the (sorted, uppercase) ticker set."""
-    canonical = ",".join(sorted(set(t.upper() for t in tickers)))
+    canonical = ",".join(sorted({t.upper() for t in tickers}))
     return hashlib.md5(canonical.encode()).hexdigest()[:12]