feat(seasonality): add the Seasonality & Session family (12 indicators) (#161)
## Summary
Adds the **Seasonality & Session** family — the first family that reads the wall-clock fields of `Candle::timestamp`. A new private `calendar` module decomposes an epoch-millisecond instant (shifted by a per-indicator `utc_offset_minutes`) into civil fields via Howard Hinnant's branch-light `civil_from_days` algorithm. Session / day / month rollovers are detected automatically, so callers never have to invoke `reset()` at a boundary.
Indicator counter **339 → 351**; family count **20 → 21**.
## Indicators
| Shape | Indicators |
|-------|-----------|
| Scalar (`f64`) | `SessionVwap`, `AverageDailyRange`, `OvernightGap`, `TurnOfMonth`, `SeasonalZScore` |
| Struct | `SessionHighLow`, `SessionRange` (Asia/EU/US), `OvernightIntradayReturn` |
| Profile (`Vec<f64>`) | `TimeOfDayReturnProfile`, `DayOfWeekProfile`, `IntradayVolatilityProfile`, `VolumeByTimeProfile` |
## Bindings
The input is the **full** candle (`open, high, low, close, volume, timestamp`), not the `high/low/close` slice the value-indicator helper assumes, so the Python / Node / WASM bindings are custom full-candle implementations:
- **Python** — `update((o,h,l,c,v,ts))`; `batch(open, high, low, close, volume, timestamp)` → `PyArray1` (scalar) / `PyArray2` (struct & profile), warmup rows `NaN`.
- **Node** — `update(open, high, low, close, volume, timestamp)`; `batch(...)` → flat `Vec<f64>`; struct outputs as `#[napi(object)]` values.
- **WASM** — `update` only (multi-input precedent); profiles as `Float64Array`, structs as camelCase objects, `timestamp` as `BigInt`.
## Verification
- `wickra-core`: full per-branch unit tests, **100%** coverage target; 2852 lib tests + 334 doctests green.
- `cargo clippy --workspace --all-targets --all-features -- -D warnings`: clean.
- Node: 428 tests (dedicated `seasonality.test.js` streaming-vs-batch).
- Python: full suite + dedicated `test_seasonality.py` streaming-vs-batch.
- Counter check: mod-count == counted lib block == 351.
kingchenc
3ab2d6ec2d