Switch from net/http to gin-gonic web framework

- Added gin-gonic v1.10.0 dependency
- Refactored router.go: clean route groups with middleware chains
- Refactored all handlers to use gin.Context instead of http.ResponseWriter/*http.Request
- Simplified response helpers (JSON, Error, Success, Created, NoContent)
- Clean auth middleware using Gin's c.Set() for context
- Cleaner route definitions with path parameters (e.g., /domains/:name/users/:id)
- Admin routes moved to /api/admin group with RequireAdmin middleware

backend/internal/api/handlers/middleware.go

@@ -1,34 +1,32 @@
 package handlers
 
 import (
-	"context"
 	"net/http"
 	"strings"
 
+	"github.com/gin-gonic/gin"
 	"github.com/imc-vibe/backend/internal/auth"
 )
 
-type contextKey string
+const AuthContextKey = "auth"
 
-const AuthContextKey contextKey = "auth"
-
-func AuthMiddleware(jwtManager *auth.JWTManager, next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		authHeader := r.Header.Get("Authorization")
+func AuthMiddleware(jwtManager *auth.JWTManager) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		authHeader := c.GetHeader("Authorization")
 		if authHeader == "" {
-			http.Error(w, `{"error":"authorization header required"}`, http.StatusUnauthorized)
+			c.AbortWithStatusJSON(http.StatusUnauthorized, Response{Error: "authorization header required"})
 			return
 		}
 
 		parts := strings.SplitN(authHeader, " ", 2)
 		if len(parts) != 2 || strings.ToLower(parts[0]) != "bearer" {
-			http.Error(w, `{"error":"invalid authorization header format"}`, http.StatusUnauthorized)
+			c.AbortWithStatusJSON(http.StatusUnauthorized, Response{Error: "invalid authorization header format"})
 			return
 		}
 
 		claims, err := jwtManager.ValidateToken(parts[1])
 		if err != nil {
-			http.Error(w, `{"error":"invalid token"}`, http.StatusUnauthorized)
+			c.AbortWithStatusJSON(http.StatusUnauthorized, Response{Error: "invalid token"})
 			return
 		}
 
@@ -38,13 +36,13 @@ func AuthMiddleware(jwtManager *auth.JWTManager, next http.Handler) http.Handler
 			Role:     auth.Role(claims.Role),
 		}
 
-		ctx := context.WithValue(r.Context(), AuthContextKey, authCtx)
-		next.ServeHTTP(w, r.WithContext(ctx))
-	})
+		c.Set(AuthContextKey, authCtx)
+		c.Next()
+	}
 }
 
-func GetAuthContext(r *http.Request) *auth.Context {
-	if ctx := r.Context().Value(AuthContextKey); ctx != nil {
+func GetAuthContext(c *gin.Context) *auth.Context {
+	if ctx, exists := c.Get(AuthContextKey); exists {
 		if authCtx, ok := ctx.(*auth.Context); ok {
 			return authCtx
 		}
@@ -52,21 +50,13 @@ func GetAuthContext(r *http.Request) *auth.Context {
 	return nil
 }
 
-func RequireAdmin(next http.Handler) http.Handler {
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		authCtx := GetAuthContext(r)
+func RequireAdmin() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		authCtx := GetAuthContext(c)
 		if authCtx == nil || !authCtx.IsAdmin() {
-			http.Error(w, `{"error":"admin access required"}`, http.StatusForbidden)
+			c.AbortWithStatusJSON(http.StatusForbidden, Response{Error: "admin access required"})
 			return
 		}
-		next.ServeHTTP(w, r)
-	})
-}
-
-func extractID(path string) string {
-	parts := strings.Split(path, "/")
-	if len(parts) > 0 {
-		return parts[len(parts)-1]
+		c.Next()
 	}
-	return ""
 }