F7: add NATR, StdDev, Ulcer Index and Historical Volatility

Completes the F7 family (Volatility) end to end:

- Rust core: natr.rs (ATR as a percentage of close), std_dev.rs
  (rolling population standard deviation), ulcer_index.rs (RMS of
  trailing-high drawdowns — downside-only risk), historical_volatility.rs
  (annualised sample stddev of log returns). Each with a full Indicator
  impl, runnable doctest and reference / constant-series / warmup /
  reset / batch==streaming tests.
- Python: PyNatr / PyStdDev / PyUlcerIndex / PyHistoricalVolatility
  PyO3 classes + module registration + .pyi stubs.
- Node: StdDevNode / UlcerIndexNode via the scalar macro, explicit
  NatrNode and HistoricalVolatilityNode; index.d.ts and index.js updated.
- WASM: WasmStdDev / WasmUlcerIndex / WasmHistoricalVolatility via the
  scalar macro, explicit WasmNatr.
- Wiki: Indicator-Natr/StdDev/UlcerIndex/HistoricalVolatility.md plus
  rows in Indicators-Overview.md and entries in Home.md.

cargo fmt + clippy (core/wickra/data/wasm/node) clean; 350 core tests,
25 data tests and 49 doctests green.

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

@@ -17,6 +17,7 @@ mod dema;
 mod donchian;
 mod dpo;
 mod ema;
+mod historical_volatility;
 mod hma;
 mod kama;
 mod keltner;
@@ -24,6 +25,7 @@ mod macd;
 mod mass_index;
 mod mfi;
 mod mom;
+mod natr;
 mod obv;
 mod pmo;
 mod ppo;
@@ -32,6 +34,7 @@ mod roc;
 mod rsi;
 mod sma;
 mod smma;
+mod std_dev;
 mod stoch_rsi;
 mod stochastic;
 mod t3;
@@ -39,6 +42,7 @@ mod tema;
 mod trima;
 mod trix;
 mod tsi;
+mod ulcer_index;
 mod ultimate_oscillator;
 mod vortex;
 mod vwap;
@@ -60,6 +64,7 @@ pub use dema::Dema;
 pub use donchian::{Donchian, DonchianOutput};
 pub use dpo::Dpo;
 pub use ema::Ema;
+pub use historical_volatility::HistoricalVolatility;
 pub use hma::Hma;
 pub use kama::Kama;
 pub use keltner::{Keltner, KeltnerOutput};
@@ -67,6 +72,7 @@ pub use macd::{MacdIndicator, MacdOutput};
 pub use mass_index::MassIndex;
 pub use mfi::Mfi;
 pub use mom::Mom;
+pub use natr::Natr;
 pub use obv::Obv;
 pub use pmo::Pmo;
 pub use ppo::Ppo;
@@ -75,6 +81,7 @@ pub use roc::Roc;
 pub use rsi::Rsi;
 pub use sma::Sma;
 pub use smma::Smma;
+pub use std_dev::StdDev;
 pub use stoch_rsi::StochRsi;
 pub use stochastic::{Stochastic, StochasticOutput};
 pub use t3::T3;
@@ -82,6 +89,7 @@ pub use tema::Tema;
 pub use trima::Trima;
 pub use trix::Trix;
 pub use tsi::Tsi;
+pub use ulcer_index::UlcerIndex;
 pub use ultimate_oscillator::UltimateOscillator;
 pub use vortex::{Vortex, VortexOutput};
 pub use vwap::{RollingVwap, Vwap};