ax(mining): replace prose comments with usage examples in service.go

Three middleware helper functions had comments that restated the function
name in prose (AX principle 2 violation). Replaced with concrete call-site
examples showing how each middleware is installed and what it does.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/service.go

@@ -181,7 +181,7 @@ func contentTypeValidationMiddleware() gin.HandlerFunc {
 	}
 }
 
-// requestIDMiddleware adds a unique request ID to each request for tracing
+// router.Use(requestIDMiddleware()) // sets X-Request-ID on every request; uses incoming header if present, otherwise generates one
 func requestIDMiddleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
 		// Use existing request ID from header if provided, otherwise generate one
@@ -209,7 +209,7 @@ func generateRequestID() string {
 	return fmt.Sprintf("%d-%s", time.Now().UnixMilli(), hex.EncodeToString(randomBytes))
 }
 
-// getRequestID extracts the request ID from gin context
+// reqID := getRequestID(c) // "" if not set, otherwise the X-Request-ID value stored by requestIDMiddleware
 func getRequestID(c *gin.Context) string {
 	if id, exists := c.Get("requestID"); exists {
 		if s, ok := id.(string); ok {
@@ -293,7 +293,7 @@ const (
 	CachePublic5Min = "public, max-age=300"
 )
 
-// cacheMiddleware adds Cache-Control headers based on the endpoint.
+// router.Use(cacheMiddleware()) // sets Cache-Control: no-store on mutating routes, max-age=30 on read-only routes
 func cacheMiddleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
 		// Only cache GET requests