fix(types): resolve all mypy type errors (CORE-003)

- Fix return type annotation for get_default_premium_for_product
- Add type narrowing for Weight|Money union using _as_money helper
- Add isinstance checks before float() calls for object types
- Add type guard for Decimal.exponent comparison
- Use _unit_typed and _currency_typed properties for type narrowing
- Cast option_type to OptionType Literal after validation
- Fix provider type hierarchy in backtesting services
- Add types-requests to dev dependencies
- Remove '|| true' from CI type-check job

All 36 mypy errors resolved across 15 files.

app/services/ltv_history.py

@@ -131,4 +131,7 @@ def _decimal_text(value: Decimal) -> str:
     if value == value.to_integral():
         return str(value.quantize(Decimal("1")))
     normalized = value.normalize()
-    return format(normalized, "f") if normalized.as_tuple().exponent < 0 else str(normalized)
+    exponent = normalized.as_tuple().exponent
+    if isinstance(exponent, int) and exponent < 0:
+        return format(normalized, "f")
+    return str(normalized)