feat(CONV-001): add GLD launch date validation, feat(DATA-DB-003): add cache CLI

CONV-001:
- Add GLD_LAUNCH_DATE constant (November 18, 2004)
- Validate reference_date in gld_ounces_per_share()
- Raise ValueError for dates before GLD launch
- Update docstring with valid date range
- Add comprehensive test coverage for edge cases

DATA-DB-003:
- Create scripts/cache_cli.py with three commands:
  - vault-dash cache stats: Show cache statistics
  - vault-dash cache list: List cached entries
  - vault-dash cache clear: Clear all cache files
- Add Makefile targets: cache-stats, cache-list, cache-clear
- Integrate with DatabentoHistoricalPriceSource methods

tests/test_databento_source.py

@@ -211,9 +211,7 @@ class TestDatabentoHistoricalPriceSource:
         assert len(result) == 4
         assert result[0].close == 185.0
 
-    def test_load_from_cache_returns_none_if_stale(
-        self, temp_cache_dir: Path, sample_ohlcv_df
-    ) -> None:
+    def test_load_from_cache_returns_none_if_stale(self, temp_cache_dir: Path, sample_ohlcv_df) -> None:
         """Returns None if cache exceeds age threshold."""
 
         source = DatabentoHistoricalPriceSource.__new__(DatabentoHistoricalPriceSource)