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/numerics/decay/Decay.md

@@ -1,5 +1,7 @@
 # DECAY: Linear Decay
 
+> *A ratchet that only moves down slowly: price can push it up instantly, but gravity pulls it back at a steady, linear pace.*
+
 | Property         | Value                            |
 | ---------------- | -------------------------------- |
 | **Category**     | Numerics                         |
@@ -16,8 +18,6 @@
 - Requires `1` bar of warmup before first valid output (IsHot = true).
 - Validated against Tulip Indicators `ti_decay` reference algorithm.
 
-> "A ratchet that only moves down slowly: price can push it up instantly, but gravity pulls it back at a steady, linear pace."
-
 DECAY implements the Tulip Indicators `ti_decay` function. When price is above the decayed level, output snaps to price. When price falls below, the output decays linearly at a rate of `1/period` per bar, creating a ceiling that gradually descends. This produces a one-sided envelope that hugs price from above.
 
 ## Historical Context