feat: init sproutclaw-web — Go+Gin backend + React frontend

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/middleware/cors.go

@@ -0,0 +1,17 @@
+package middleware
+
+import "github.com/gin-gonic/gin"
+
+// CORS allows all origins (needed for desktop clients and dev server proxy).
+func CORS() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Header("Access-Control-Allow-Origin", "*")
+		c.Header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS")
+		c.Header("Access-Control-Allow-Headers", "Content-Type, Authorization")
+		if c.Request.Method == "OPTIONS" {
+			c.AbortWithStatus(204)
+			return
+		}
+		c.Next()
+	}
+}