feat(dynamics): add PlusDI, MinusDI, PlusDM, MinusDM indicators

Complete thin Dx-composition wrapper indicators with full test coverage:

- PlusDi/MinusDi: Directional Indicator wrappers (DiPlus/DiMinus from Dx)
- PlusDm/MinusDm: Directional Movement wrappers (DmPlus/DmMinus from Dx)
- Individual validation tests per indicator directory (TALib, Skender, bounds)
- Combined unit tests (DiDm.Tests.cs) and validation tests (DiDm.Validation.Tests.cs)
- Quantower wrappers + tests for all 4 indicators
- PineScript v6 implementations with compensated RMA
- Normalized .md documentation for all indicators and categories
- 182 tests passing, 0 failures

lib/statistics/stderr/Stderr.md

@@ -1,5 +1,7 @@
 # Stderr: Standard Error of Regression
 
+> *How confident are you in your line of best fit?*
+
 | Property         | Value                            |
 | ---------------- | -------------------------------- |
 | **Category**     | Statistic                        |
@@ -16,8 +18,6 @@
 - Requires `period` bars of warmup before first stable output (`IsHot = true`).
 - Validated against an internal brute-force OLS reference implementation.
 
-> "How confident are you in your line of best fit?"
-
 Standard Error of Regression (also called the Standard Error of the Estimate) measures the average distance that the observed values fall from the regression line. It quantifies the typical size of the residuals, providing a direct measure of how well a linear regression model fits the data.
 
 ## Historical Context