Provider abstraction: providers/ package with BaseDataProvider template

One class per provider (TwelveData, Oanda, Tiingo), all subclassing
BaseDataProvider which owns cache, validation/cleaning, freshness +
boundary guarantees, fetch_range pagination, and streaming stubs —
subclasses implement only _fetch_raw. config.json data_providers.active
selects the live feed; data_provider.py / oanda_provider.py stay as
back-compat shims. Module 16 provider-abstraction tests (253 total green).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Mc7XKYyPySVXiUpcN82QEK

signal_aggregator.py

@@ -15,7 +15,7 @@ import pandas as pd
 
 from chart_patterns import detect_chart_pattern
 from config import PlatformConfig, SignalStrength, Timeframe
-from data_provider import ForexDataProvider, make_data_provider
+from providers import BaseDataProvider, make_data_provider
 from engine import TechnicalEngine, TechnicalAnalysis
 from news_engine import NewsEngine, FundamentalContext
 
@@ -180,7 +180,7 @@ class SignalAggregator:
             try:
                 df = self.data_provider.fetch_ohlcv(symbol, tf)
                 dfs[tf] = df
-                if not self.data_provider._is_data_fresh(df, symbol, tf):
+                if not self.data_provider.is_data_fresh(df, symbol, tf):
                     stale_tfs.append(tf.value)
             except Exception as e:
                 logger.warning(f"Fetch failed for {symbol} {tf.value}: {e}")
@@ -214,7 +214,7 @@ class SignalAggregator:
                 bar_close = (
                     pd.Timestamp(report.timestamp)
                     + pd.Timedelta(
-                        seconds=ForexDataProvider.CANDLE_SECONDS[
+                        seconds=BaseDataProvider.CANDLE_SECONDS[
                             self.config.primary_timeframe
                         ]
                     )
@@ -637,7 +637,7 @@ class SignalAggregator:
                     close_h = (
                         pd.Timestamp(report.timestamp)
                         + pd.Timedelta(
-                            seconds=ForexDataProvider.CANDLE_SECONDS[
+                            seconds=BaseDataProvider.CANDLE_SECONDS[
                                 self.config.primary_timeframe
                             ]
                         )
@@ -939,7 +939,7 @@ class SignalAggregator:
                     close_h = (
                         pd.Timestamp(report.timestamp)
                         + pd.Timedelta(
-                            seconds=ForexDataProvider.CANDLE_SECONDS[
+                            seconds=BaseDataProvider.CANDLE_SECONDS[
                                 self.config.primary_timeframe
                             ]
                         )