feat: 15 funciones finance — indicadores, riesgo e IO de mercado

11 funciones puras con implementación real:
SMA, EMA, RSI, BollingerBands, VWAP, LogReturn, AnnualizedVolatility,
SharpeRatio, MaxDrawdown, NormalizeOHLCV, TickToOHLCV

4 funciones impuras (stubs):
FetchOHLCV, StreamTicks, WriteOHLCVToParquet, LoadOHLCVFromDuckDB

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

functions/finance/rsi.md

@@ -0,0 +1,31 @@
+---
+name: rsi
+kind: function
+lang: go
+domain: finance
+version: "1.0.0"
+purity: pure
+signature: "func RSI(data []float64, period int) []float64"
+description: "Calcula el Relative Strength Index (RSI) usando suavizado de Wilder."
+tags: [finance, indicator, rsi, momentum]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: []
+tested: false
+tests: []
+test_file_path: ""
+file_path: "functions/finance/rsi.go"
+---
+
+# rsi
+
+Calcula el Relative Strength Index (RSI) con el metodo de suavizado de Wilder. Los primeros `period` elementos son 0. El RSI oscila entre 0 y 100.
+
+## Ejemplo
+
+```go
+result := finance.RSI([]float64{44, 44.34, 44.09, 43.61, 44.33, 44.83, 45.10, 45.42, 45.84}, 5)
+```