F8: add Bollinger Bandwidth and %b

Completes the F8 family (Bands & channels) end to end:

- Rust core: bollinger_bandwidth.rs ((upper - lower) / middle — the
  squeeze gauge) and percent_b.rs ((price - lower) / (upper - lower) —
  price position within the bands, unclamped). Both wrap BollingerBands
  and carry a full Indicator impl, runnable doctest and reference /
  constant-series / definition-consistency / warmup / reset /
  batch==streaming tests.
- Python: PyBollingerBandwidth / PyPercentB PyO3 classes + module
  registration + .pyi stubs (defaults (20, 2.0)).
- Node: explicit BollingerBandwidthNode and PercentBNode; index.d.ts
  and index.js updated.
- WASM: WasmBollingerBandwidth / WasmPercentB via the scalar macro.
- Wiki: Indicator-BollingerBandwidth.md and Indicator-PercentB.md plus
  rows in Indicators-Overview.md and entries in Home.md.

cargo fmt + clippy (core/wickra/data/wasm/node) clean; 362 core tests,
25 data tests and 51 doctests green.

docs/wiki/Home.md

@@ -122,6 +122,8 @@ Rust / Python / Node examples. They are grouped by family, mirroring the
 - [Indicator-StdDev.md](indicators/volatility/Indicator-StdDev.md)
 - [Indicator-UlcerIndex.md](indicators/volatility/Indicator-UlcerIndex.md)
 - [Indicator-HistoricalVolatility.md](indicators/volatility/Indicator-HistoricalVolatility.md)
+- [Indicator-BollingerBandwidth.md](indicators/volatility/Indicator-BollingerBandwidth.md)
+- [Indicator-PercentB.md](indicators/volatility/Indicator-PercentB.md)
 
 **Volume** — price moves weighted or confirmed by traded volume.