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/spearman/Spearman.md

@@ -1,5 +1,7 @@
 # SPEARMAN: Spearman Rank Correlation Coefficient
 
+> *The person who asks whether rank correlation exists is not asking a wholly foolish question.*
+
 | Property         | Value                            |
 | ---------------- | -------------------------------- |
 | **Category**     | Statistic                        |
@@ -16,8 +18,6 @@
 - Requires `period` bars of warmup before first valid output (IsHot = true).
 - Validated against TA-Lib, Skender, and Tulip reference implementations where available.
 
-> "The person who asks whether rank correlation exists is not asking a wholly foolish question." — Maurice Kendall (1970)
-
 Spearman's ρ (rho) measures the strength and direction of monotonic association between two variables. Unlike Pearson's correlation, which measures linear relationship, Spearman captures any monotonic relationship. A portfolio of stocks whose returns move monotonically together has different risk than one whose components merely share a linear trend. Spearman detects both.
 
 ## Historical Context