F6: add Aroon Oscillator, Vortex and Mass Index

Completes the F6 family (Trend strength) end to end:

- Rust core: aroon_oscillator.rs (AroonUp - AroonDown, one-line trend
  gauge), vortex.rs (Vortex Indicator VI+/VI- with the VortexOutput
  struct), mass_index.rs (Dorsey's range-expansion sum of the
  EMA-of-range ratio). Each with a full Indicator impl, runnable doctest
  and reference / saturation / warmup / reset / batch==streaming tests.
- Python: PyAroonOscillator / PyVortex / PyMassIndex PyO3 classes +
  module registration + .pyi stubs (defaults Aroon=14, Vortex=14,
  MassIndex=(9,25)).
- Node: explicit AroonOscillatorNode, VortexNode (with VortexValue
  object) and MassIndexNode; index.d.ts and index.js updated.
- WASM: WasmAroonOscillator, WasmVortex, WasmMassIndex.
- Wiki: Indicator-AroonOscillator/Vortex/MassIndex.md plus rows in
  Indicators-Overview.md and entries in Home.md.

cargo fmt + clippy (core/wickra/data/wasm/node) clean; 320 core tests,
25 data tests and 45 doctests green.

crates/wickra-core/src/lib.rs

@@ -44,11 +44,11 @@ pub mod indicators;
 
 pub use error::{Error, Result};
 pub use indicators::{
-    Adx, AdxOutput, Aroon, AroonOutput, Atr, AwesomeOscillator, BollingerBands, BollingerOutput,
-    Cci, Cmo, Coppock, Dema, Donchian, DonchianOutput, Dpo, Ema, Hma, Kama, Keltner, KeltnerOutput,
-    MacdIndicator, MacdOutput, Mfi, Mom, Obv, Pmo, Ppo, Psar, Roc, RollingVwap, Rsi, Sma, Smma,
-    StochRsi, Stochastic, StochasticOutput, Tema, Trima, Trix, Tsi, UltimateOscillator, Vwap, Vwma,
-    WilliamsR, Wma, Zlema, T3,
+    Adx, AdxOutput, Aroon, AroonOscillator, AroonOutput, Atr, AwesomeOscillator, BollingerBands,
+    BollingerOutput, Cci, Cmo, Coppock, Dema, Donchian, DonchianOutput, Dpo, Ema, Hma, Kama,
+    Keltner, KeltnerOutput, MacdIndicator, MacdOutput, MassIndex, Mfi, Mom, Obv, Pmo, Ppo, Psar,
+    Roc, RollingVwap, Rsi, Sma, Smma, StochRsi, Stochastic, StochasticOutput, Tema, Trima, Trix,
+    Tsi, UltimateOscillator, Vortex, VortexOutput, Vwap, Vwma, WilliamsR, Wma, Zlema, T3,
 };
 pub use ohlcv::{Candle, Tick};
 pub use traits::{BatchExt, Chain, Indicator};