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).

Claude-Session: https://claude.ai/code/session_01Mc7XKYyPySVXiUpcN82QEK

providers/__init__.py

@@ -0,0 +1,54 @@
+"""
+ForexBot2 — Data-provider package
+==================================
+One class per provider, all subclassing `BaseDataProvider` (which owns
+caching, validation, boundary guarantees, and range pagination — the
+behavior the signal pipeline depends on).
+
+Adding a provider = one module implementing `_fetch_raw` + one registry
+entry + one config.json `data_providers` block. The live feed is selected
+by config.json `data_providers.active`; registration alone changes
+nothing.
+"""
+
+from typing import Dict
+
+from app_config import AppConfigError, get_app_config
+from config import PlatformConfig
+
+from providers.base import BaseDataProvider, DataIntegrityError, _is_forex_weekend
+from providers.twelve_data import TwelveDataProvider
+from providers.oanda import OandaDataError, OandaDataProvider
+from providers.tiingo import TiingoDataError, TiingoDataProvider
+
+#: config.json data_providers.active selects from here.
+PROVIDER_REGISTRY: Dict[str, type] = {
+    "twelve_data": TwelveDataProvider,
+    "oanda": OandaDataProvider,
+    "tiingo": TiingoDataProvider,
+}
+
+
+def make_data_provider(config: PlatformConfig) -> BaseDataProvider:
+    """Build the ACTIVE data provider (config.json: data_providers.active)."""
+    name = get_app_config().active_provider
+    cls = PROVIDER_REGISTRY.get(name)
+    if cls is None:
+        raise AppConfigError(
+            f'Unknown data provider "{name}"; '
+            f"registered: {sorted(PROVIDER_REGISTRY)}")
+    return cls(config)
+
+
+__all__ = [
+    "BaseDataProvider",
+    "DataIntegrityError",
+    "OandaDataError",
+    "OandaDataProvider",
+    "TiingoDataError",
+    "TiingoDataProvider",
+    "TwelveDataProvider",
+    "PROVIDER_REGISTRY",
+    "make_data_provider",
+    "_is_forex_weekend",
+]