feat: add fetch_latest_closed_rates_indexed and allow_whole_dollar_env opt-in (#45)

* feat: add fetch_latest_closed_rates_indexed and allow_whole_dollar_env opt-in (#43, #44)

Closes #43: add fetch_latest_closed_rates_indexed(client, *, symbol,
granularity, count) -> pd.DataFrame to mt5cli/trading.py. Internally
reuses fetch_latest_closed_rates_for_trading_client(), converts the
"time" column to a UTC-aware DatetimeIndex named "time", and drops the
original column. Exported from trading.__all__, mt5cli.__init__, and
STABLE_SDK_EXPORTS.

Closes #44: extend substitute_env_placeholders() with opt-in
allow_whole_dollar_env=False that expands whole-value $ENV_NAME strings
(entire string must be exactly $IDENTIFIER). Threaded through
build_config(), resolve_account_spec(), and resolve_account_specs() with
the same default=False. Partial strings like "plan$pass", "abc$ENV", or
"$ENV-suffix" are never expanded.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* chore: align Markdown table columns in docs and skill file

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: treat numeric (float64) epoch seconds as UTC in _rate_time_to_utc

After DataFrame concat or NA upcast the time column becomes float64, which
is still epoch seconds. Using is_numeric_dtype instead of is_integer_dtype
fixes the silent misalignment. Using series.to_numpy() before passing to
pd.to_datetime avoids the redundant pd.DatetimeIndex() wrapper and aligns
with how existing rate-time normalization in schemas.py handles numeric
timestamps.

Add test_converts_float_epoch_seconds_to_utc_datetime_index to cover the
regression. Add a doc note clarifying that build_config cannot expand
login since that parameter is int | None.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: reject NaT values after rate timestamp conversion in _rate_time_to_utc

pd.to_datetime() silently produces NaT for None/NaN inputs rather than
raising, so the function could return a DatetimeIndex containing NaT
despite documenting invalid timestamps as a ValueError. Check any(idx.isna())
after conversion and raise with a clear message.

Add test_raises_on_nat_time_column to cover the regression.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* Bump version to v0.9.0

* fix: handle object numeric rate timestamps

---------

Co-authored-by: Claude <noreply@anthropic.com>

tests/test_contracts.py

@@ -44,6 +44,7 @@ from mt5cli import (
     export_dataframe_to_sqlite,
     fetch_latest_closed_rates,
     fetch_latest_closed_rates_for_trading_client,
+    fetch_latest_closed_rates_indexed,
     granularity_name,
     is_recoverable_mt5_error,
     load_rate_data,
@@ -734,3 +735,32 @@ class TestStableSdkContract:
             raise RuntimeError(message)
 
         mock_client.shutdown.assert_called_once()
+
+    def test_fetch_latest_closed_rates_indexed_from_package_root(
+        self,
+        mocker: MockerFixture,
+    ) -> None:
+        """Indexed closed-bar helper returns a UTC DatetimeIndex named 'time'."""
+        client = MagicMock()
+        mocker.patch(
+            "mt5cli.trading.fetch_latest_closed_rates_for_trading_client",
+            return_value=pd.DataFrame(
+                {
+                    "time": [1704067200, 1704153600, 1704240000],
+                    "close": [1.0, 1.1, 1.2],
+                },
+            ),
+        )
+
+        result = fetch_latest_closed_rates_indexed(
+            client,
+            symbol="EURUSD",
+            granularity="M1",
+            count=2,
+        )
+
+        assert isinstance(result.index, pd.DatetimeIndex)
+        assert result.index.name == "time"
+        assert result.index.tz is not None
+        assert "time" not in result.columns
+        assert "close" in result.columns