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/stats.go

@@ -1,8 +1,7 @@
 package handlers
 
 import (
-	"net/http"
-
+	"github.com/gin-gonic/gin"
 	"github.com/imc-vibe/backend/internal/db"
 )
 
@@ -21,12 +20,7 @@ type Stats struct {
 	QueueSize    int `json:"queueSize"`
 }
 
-func (h *StatsHandler) Get(w http.ResponseWriter, r *http.Request) {
-	if r.Method != http.MethodGet {
-		Error(w, http.StatusMethodNotAllowed, "method not allowed")
-		return
-	}
-
+func (h *StatsHandler) Get(c *gin.Context) {
 	domains, err := h.db.GetAllDomains()
 	if err != nil {
 		domains = []db.DomainStats{}
@@ -49,5 +43,5 @@ func (h *StatsHandler) Get(w http.ResponseWriter, r *http.Request) {
 		QueueSize:    0,
 	}
 
-	Success(w, stats)
+	Success(c, stats)
 }