feat(data): add FRED macro indicators as an optional vendor

Surface Federal Reserve Economic Data (rates, inflation, labor, growth) to the
news analyst via a new get_macro_indicators tool and a macro_data vendor
category. Friendly aliases (cpi, unemployment, fed_funds_rate, 10y_treasury,
yield_curve, ...) map to FRED series IDs; raw series IDs are accepted too. The
report gives the latest value, change over the window, and a recent observation
table. Windowing is lookahead-safe (observation_end = curr_date), missing values
are skipped, and a missing FRED_API_KEY surfaces as a clear not-configured
condition through the vendor router rather than a crash.

tradingagents/default_config.py

@@ -106,6 +106,7 @@ DEFAULT_CONFIG = _apply_env_overrides({
         "technical_indicators": "yfinance",  # Options: alpha_vantage, yfinance
         "fundamental_data": "yfinance",      # Options: alpha_vantage, yfinance
         "news_data": "yfinance",             # Options: alpha_vantage, yfinance
+        "macro_data": "fred",                # Options: fred (needs FRED_API_KEY)
     },
     # Tool-level configuration (takes precedence over category-level)
     "tool_vendors": {