F12: add price transforms and rolling linear regression

- Rust core: typical_price.rs ((H+L+C)/3), median_price.rs ((H+L)/2),
  weighted_close.rs ((H+L+2C)/4) — stateless per-bar OHLC transforms — and
  linreg.rs (LinearRegression — endpoint of a rolling ordinary-least-squares
  fit) and linreg_slope.rs (LinRegSlope — slope of that fit). Each with a
  full Indicator impl, runnable doctest and reference / property / warmup /
  reset / batch==streaming tests.
- Python: PyTypicalPrice / PyMedianPrice / PyWeightedClose /
  PyLinearRegression / PyLinRegSlope PyO3 classes + module registration +
  .pyi stubs.
- Node: explicit TypicalPriceNode / MedianPriceNode / WeightedCloseNode /
  LinearRegressionNode / LinRegSlopeNode; index.d.ts and index.js updated.
- WASM: explicit WasmTypicalPrice / WasmMedianPrice / WasmWeightedClose;
  WasmLinearRegression / WasmLinRegSlope via the scalar macro.
- Wiki: a new indicators/statistics/ folder with five Indicator-*.md pages,
  a new "Statistics" family in Indicators-Overview.md and Home.md.

cargo fmt + clippy (core/wickra/data/wasm/node) clean; 454 core tests,
25 data tests and 66 doctests green.

crates/wickra-core/src/indicators/mod.rs

@@ -30,8 +30,11 @@ mod historical_volatility;
 mod hma;
 mod kama;
 mod keltner;
+mod linreg;
+mod linreg_slope;
 mod macd;
 mod mass_index;
+mod median_price;
 mod mfi;
 mod mom;
 mod natr;
@@ -53,12 +56,14 @@ mod tema;
 mod trima;
 mod trix;
 mod tsi;
+mod typical_price;
 mod ulcer_index;
 mod ultimate_oscillator;
 mod vortex;
 mod vpt;
 mod vwap;
 mod vwma;
+mod weighted_close;
 mod williams_r;
 mod wma;
 mod zlema;
@@ -89,8 +94,11 @@ pub use historical_volatility::HistoricalVolatility;
 pub use hma::Hma;
 pub use kama::Kama;
 pub use keltner::{Keltner, KeltnerOutput};
+pub use linreg::LinearRegression;
+pub use linreg_slope::LinRegSlope;
 pub use macd::{MacdIndicator, MacdOutput};
 pub use mass_index::MassIndex;
+pub use median_price::MedianPrice;
 pub use mfi::Mfi;
 pub use mom::Mom;
 pub use natr::Natr;
@@ -112,12 +120,14 @@ pub use tema::Tema;
 pub use trima::Trima;
 pub use trix::Trix;
 pub use tsi::Tsi;
+pub use typical_price::TypicalPrice;
 pub use ulcer_index::UlcerIndex;
 pub use ultimate_oscillator::UltimateOscillator;
 pub use vortex::{Vortex, VortexOutput};
 pub use vpt::VolumePriceTrend;
 pub use vwap::{RollingVwap, Vwap};
 pub use vwma::Vwma;
+pub use weighted_close::WeightedClose;
 pub use williams_r::WilliamsR;
 pub use wma::Wma;
 pub use zlema::Zlema;