feat: add 8 new indicators with full integration

New indicators:
- HWC (Holt-Winters Channel) — channels, 27 tests
- VWMACD (Volume-Weighted MACD) — momentum, 38 tests
- Squeeze Pro — oscillators, 69 tests
- BW_MFI (Bill Williams MFI) — oscillators
- DSTOCH (Double Stochastic) — oscillators
- ATRSTOP (ATR Trailing Stop) — reversals
- VSTOP (Volatility Stop) — reversals
- Convexity (Beta Convexity) — statistics, 23 tests

Integration:
- Python bridge: Exports.cs, _bridge.py, wrapper modules
- Documentation: _sidebar.md, _index.md pages, SPEC.md
- All analyzer warnings fixed (MA0074, xUnit2013, S2699)

Build: 0 warnings, 0 errors | Tests: 15,933 passed, 0 failed

_sidebar.md

@@ -130,6 +130,7 @@
   * [BBI - Bulls Bears Index](/lib/oscillators/bbi/Bbi.md)
   * [BBS - Bollinger Band Squeeze](/lib/oscillators/bbs/Bbs.md)
   * [BRAR - Bull-Bear Power Ratio](/lib/oscillators/brar/Brar.md)
+  * [BW_MFI - Bill Williams MFI](/lib/oscillators/bw_mfi/BwMfi.md)
   * [CFO - Chande Forecast Oscillator](/lib/oscillators/cfo/Cfo.md)
   * [COPPOCK - Coppock Curve](/lib/oscillators/coppock/Coppock.md)
   * [CRSI - Connors RSI](/lib/oscillators/crsi/Crsi.md)
@@ -138,6 +139,7 @@
   * [DEM - DeMarker Oscillator](/lib/oscillators/dem/Dem.md)
   * [DOSC - Derivative Oscillator](/lib/oscillators/dosc/Dosc.md)
   * [DPO - Detrended Price Oscillator](/lib/oscillators/dpo/Dpo.md)
+  * [DSTOCH - Double Stochastic (Bressert)](/lib/oscillators/dstoch/Dstoch.md)
   * [DYMI - Dynamic Momentum Index](/lib/oscillators/dymi/dymi.md)
   * [ER - Efficiency Ratio](/lib/oscillators/er/Er.md)
   * [ERI - Elder Ray Index](/lib/oscillators/eri/Eri.md)
@@ -161,6 +163,7 @@
   * [RVGI - Relative Vigor Index](/lib/oscillators/rvgi/Rvgi.md)
   * [SMI - Stochastic Momentum Index](/lib/oscillators/smi/Smi.md)
   * [SQUEEZE - Squeeze Momentum](/lib/oscillators/squeeze/Squeeze.md)
+  * [SQUEEZE_PRO - Squeeze Pro](/lib/oscillators/squeeze_pro/squeeze_pro.md)
   * [STC - Schaff Trend Cycle](/lib/oscillators/stc/Stc.md)
   * [STOCH - Stochastic Oscillator](/lib/oscillators/stoch/Stoch.md)
   * [STOCHF - Stochastic Fast](/lib/oscillators/stochf/Stochf.md)
@@ -218,6 +221,7 @@
   * [RSX - Jurik Relative Strength X](/lib/momentum/rsx/Rsx.md)
   * [SAM - Smoothed Adaptive Momentum](/lib/momentum/sam/Sam.md)
   * [TSI - True Strength Index](/lib/momentum/tsi/Tsi.md)
+  * [VWMACD - Volume-Weighted MACD](/lib/momentum/vwmacd/Vwmacd.md)
   * [VEL - Jurik Velocity](/lib/momentum/vel/Vel.md)
 
 * [Volatility](/lib/volatility/_index.md)
@@ -287,6 +291,7 @@
   * [DC - Donchian Channels](/lib/channels/dc/dc.md)
   * [DECAYCHANNEL - Decay Min-Max Channel](/lib/channels/decaychannel/decaychannel.md)
   * [FCB - Fractal Chaos Bands](/lib/channels/fcb/Fcb.md)
+  * [HWC - Holt-Winters Channel](/lib/channels/hwc/Hwc.md)
   * [JBANDS - Jurik Volatility Bands](/lib/channels/jbands/Jbands.md)
   * [KC - Keltner Channel](/lib/channels/kc/Kc.md)
   * [MAENV - Moving Average Envelope](/lib/channels/maenv/Maenv.md)
@@ -319,6 +324,7 @@
   * [SSFDSP - Ehlers SSF Detrended Synthetic Price](/lib/cycles/ssfdsp/Ssfdsp.md)
 
 * [Reversals](/lib/reversals/_index.md)
+  * [ATRSTOP - ATR Trailing Stop](/lib/reversals/atrstop/Atrstop.md)
   * [CHANDELIER - Chandelier Exit](/lib/reversals/chandelier/Chandelier.md)
   * [CKSTOP - Chande Kroll Stop](/lib/reversals/ckstop/Ckstop.md)
   * [FRACTALS - Williams Fractals](/lib/reversals/fractals/Fractals.md)
@@ -332,6 +338,7 @@
   * [SAREXT - Parabolic SAR Extended](/lib/reversals/sarext/Sarext.md)
   * [SWINGS - Swing High/Low Detection](/lib/reversals/swings/Swings.md)
   * [TTM_SCALPER - TTM Scalper Alert](/lib/reversals/ttm_scalper/TtmScalper.md)
+  * [VSTOP - Volatility Stop](/lib/reversals/vstop/Vstop.md)
 
 * [Forecasts](/lib/forecasts/_index.md)
   * [AFIRMA - Adaptive FIR MA](/lib/forecasts/afirma/Afirma.md)
@@ -342,6 +349,7 @@
   * [BETA - Beta Coefficient](/lib/statistics/beta/Beta.md)
   * [CMA - Cumulative MA](/lib/statistics/cma/Cma.md)
   * [COINTEGRATION - Cointegration](/lib/statistics/cointegration/Cointegration.md)
+  * [CONVEXITY - Beta Convexity](/lib/statistics/convexity/Convexity.md)
   * [CORREL - Correlation](/lib/statistics/correl/Correl.md)
   * [COVARIANCE - Covariance](/lib/statistics/covariance/Covariance.md)
   * [ENTROPY - Shannon Entropy](/lib/statistics/entropy/Entropy.md)