refactor: use 'c' alias for constants package

- Update all imports from 'constants' to 'c' for brevity
- Replace all 'constants.' references with 'c.'
- Fix remaining hardcoded content-type headers in httputil
- Fix remaining hardcoded User-Agent and Accept headers
- Rename CSRF receiver from 'c' to 'csrf' to avoid conflict
- Add ContentTypePlainSimple constant for Accept header matching
- Fix JSONCached to use proper integer formatting

internal/middleware/security_logger.go

@@ -8,7 +8,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/juanatsap/cv-site/internal/constants"
+	c "github.com/juanatsap/cv-site/internal/constants"
 )
 
 // SecurityEvent represents a security-related event
@@ -57,7 +57,7 @@ func LogSecurityEvent(eventType string, r *http.Request, details string) {
 		EventType: eventType,
 		Severity:  severity,
 		IP:        getClientIP(r),
-		UserAgent: r.Header.Get(constants.HeaderUserAgent),
+		UserAgent: r.Header.Get(c.HeaderUserAgent),
 		Method:    r.Method,
 		Path:      r.URL.Path,
 		Details:   details,
@@ -74,7 +74,7 @@ func LogSecurityEvent(eventType string, r *http.Request, details string) {
 	log.Printf("[SECURITY] %s", eventJSON)
 
 	// Also log to separate security log file in production
-	if os.Getenv(constants.EnvVarGOEnv) == constants.EnvProduction {
+	if os.Getenv(c.EnvVarGOEnv) == c.EnvProduction {
 		logToSecurityFile(eventJSON)
 	}
 }
@@ -99,14 +99,14 @@ func getSeverity(eventType string) string {
 // getClientIP extracts the real client IP from request headers
 func getClientIP(r *http.Request) string {
 	// Check X-Forwarded-For header (proxy/load balancer)
-	if xff := r.Header.Get(constants.HeaderXForwardedFor); xff != "" {
+	if xff := r.Header.Get(c.HeaderXForwardedFor); xff != "" {
 		// Take first IP from comma-separated list
 		ips := strings.Split(xff, ",")
 		return strings.TrimSpace(ips[0])
 	}
 
 	// Check X-Real-IP header
-	if xri := r.Header.Get(constants.HeaderXRealIP); xri != "" {
+	if xri := r.Header.Get(c.HeaderXRealIP); xri != "" {
 		return xri
 	}
 
@@ -181,7 +181,7 @@ func SecurityLogger(next http.Handler) http.Handler {
 				EventType: "REQUEST",
 				Severity:  SeverityInfo,
 				IP:        getClientIP(r),
-				UserAgent: r.Header.Get(constants.HeaderUserAgent),
+				UserAgent: r.Header.Get(c.HeaderUserAgent),
 				Method:    r.Method,
 				Path:      r.URL.Path,
 				Details:   string(detailsJSON),
@@ -203,7 +203,7 @@ func SecurityLogger(next http.Handler) http.Handler {
 				EventType: "HTTP_ERROR",
 				Severity:  severity,
 				IP:        getClientIP(r),
-				UserAgent: r.Header.Get(constants.HeaderUserAgent),
+				UserAgent: r.Header.Get(c.HeaderUserAgent),
 				Method:    r.Method,
 				Path:      r.URL.Path,
 				Details:   http.StatusText(wrapped.status),