Security: add rate limiting, input validation, and filter category

validation
Backend:
- Add rate limiting middleware (mw/ratelimit.go) - in-memory per-IP
  limiter
- Apply rate limits per endpoint group:
  - Public read-only: 120/min
  - Registration: 10/min
  - Portfolio filters: 60/min
  - Authenticated users: 120/min
  - Admin: none (trusted)
- Add 256 char input length validation on portfolio endpoints
- Validate filter categories exist in DB before querying
- Secure GetImage endpoint: only allow UUID or numeric timestamp (15-20
  digits)
- Remove pattern-based image lookup to prevent enumeration
- Add services validation: name (100), duration (1-480), patch test
  (0-168)
  Frontend:
- Add maxlength=256 to portfolio tag/search inputs
- Add maxlength to registration: name (50), email (255), phone (20),
  password (72)
- Add maxlength=100 to service name input

backend/mw/ratelimit.go

@@ -0,0 +1,95 @@
+package mw
+
+import (
+	"net/http"
+	"sync"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// RateLimiter implements a simple in-memory rate limiter
+type RateLimiter struct {
+	requests map[string][]time.Time
+	mu       sync.RWMutex
+	limit    int
+	window   time.Duration
+}
+
+func NewRateLimiter(limit int, window time.Duration) *RateLimiter {
+	rl := &RateLimiter{
+		requests: make(map[string][]time.Time),
+		limit:    limit,
+		window:   window,
+	}
+	// Cleanup old entries periodically
+	go func() {
+		for {
+			time.Sleep(window)
+			rl.cleanup()
+		}
+	}()
+	return rl
+}
+
+func (rl *RateLimiter) cleanup() {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+	now := time.Now()
+	for key, times := range rl.requests {
+		var valid []time.Time
+		for _, t := range times {
+			if now.Sub(t) < rl.window {
+				valid = append(valid, t)
+			}
+		}
+		if len(valid) == 0 {
+			delete(rl.requests, key)
+		} else {
+			rl.requests[key] = valid
+		}
+	}
+}
+
+func (rl *RateLimiter) Allow(key string) bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+	now := time.Now()
+	windowStart := now.Add(-rl.window)
+
+	var valid []time.Time
+	for _, t := range rl.requests[key] {
+		if t.After(windowStart) {
+			valid = append(valid, t)
+		}
+	}
+
+	if len(valid) >= rl.limit {
+		rl.requests[key] = valid
+		return false
+	}
+
+	rl.requests[key] = append(valid, now)
+	return true
+}
+
+// RateLimit middleware - limits requests per IP
+func RateLimit(limit int, window time.Duration) func(http.Handler) http.Handler {
+	limiter := NewRateLimiter(limit, window)
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			// Get client IP
+			ip := chi.URLParam(r, "X-Real-IP")
+			if ip == "" {
+				ip = r.RemoteAddr
+			}
+
+			if !limiter.Allow(ip) {
+				http.Error(w, "Rate limit exceeded", http.StatusTooManyRequests)
+				return
+			}
+
+			next.ServeHTTP(w, r)
+		})
+	}
+}