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/vwap.md

@@ -0,0 +1,32 @@
+---
+name: vwap
+kind: function
+lang: go
+domain: finance
+version: "1.0.0"
+purity: pure
+signature: "func VWAP(prices, volumes []float64) float64"
+description: "Calcula el Volume Weighted Average Price (VWAP) a partir de precios y volumenes."
+tags: [finance, indicator, vwap, volume]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: ""
+imports: []
+tested: false
+tests: []
+test_file_path: ""
+file_path: "functions/finance/vwap.go"
+---
+
+# vwap
+
+Calcula el VWAP (Volume Weighted Average Price). Es la suma de (precio * volumen) dividida por la suma de volumenes.
+
+## Ejemplo
+
+```go
+v := finance.VWAP([]float64{100, 102, 101}, []float64{500, 300, 200})
+// v = (100*500 + 102*300 + 101*200) / (500+300+200)
+```