fix: audit round 3 — IDOR report-scoping, auth rate-limit, briefing chat scoping, DailyVolumes dedup, N+1 list routines, FE export/ask error handling

- IDOR: interrogate without report_id now scoped to user_key (LatestReportForUser); regression test TestInterrogateIDORScoped
- auth: signup/login per-IP rate limit 10/60s (new internal/api/ratelimit.go) + test
- chat unscoped grounding: build caller's own briefing instead of global LatestBriefing
- DailyVolumes: dedupe by bar date (snapshot rows hold 30-day windows) — fixes volume-anomaly skew
- GetDestination: direct (id,user_key) query instead of listing all
- ListRoutines: single LastRunsByRoutine query instead of N+1 RunHistory
- FE: exportMd/ask/HTML/PDF export now surface errors; alerts create clears channels

backend/internal/api/ratelimit.go

@@ -0,0 +1,93 @@
+// Package api — rate limit helpers for auth endpoints.
+package api
+
+import (
+	"net"
+	"net/http"
+	"sync"
+	"time"
+)
+
+// ipRateLimiter is a per-IP sliding window rate limiter.
+type ipRateLimiter struct {
+	mu       sync.Mutex
+	windows  map[string]*window
+	limit    int
+	windowSz time.Duration
+}
+
+type window struct {
+	hits    []time.Time
+}
+
+func newIPRateLimiter(limit int, windowSz time.Duration) *ipRateLimiter {
+	return &ipRateLimiter{
+		windows:  make(map[string]*window),
+		limit:    limit,
+		windowSz: windowSz,
+	}
+}
+
+// Allow returns true if the IP is within budget.
+func (rl *ipRateLimiter) Allow(ip string) bool {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+
+	now := time.Now()
+	w, ok := rl.windows[ip]
+	if !ok {
+		w = &window{}
+		rl.windows[ip] = w
+	}
+	// Trim entries outside the window.
+	cutoff := now.Add(-rl.windowSz)
+	n := 0
+	for _, t := range w.hits {
+		if t.After(cutoff) {
+			w.hits[n] = t
+			n++
+		}
+	}
+	w.hits = w.hits[:n]
+	if len(w.hits) >= rl.limit {
+		return false
+	}
+	w.hits = append(w.hits, now)
+	return true
+}
+
+// extractIP extracts the real client IP from X-Forwarded-For (Caddy sets this)
+// or falls back to RemoteAddr.
+func extractIP(r *http.Request) string {
+	if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
+		// First IP in the chain is the original client.
+		if ip := net.ParseIP(xff[:len(xff)]); ip != nil {
+			return xff
+		}
+		// Handle comma-separated: take first.
+		for i := 0; i < len(xff); i++ {
+			if xff[i] == ',' {
+				return xff[:i]
+			}
+		}
+		return xff
+	}
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}
+
+// rateLimitAuth is middleware that limits auth-related endpoints per IP:
+// max requests per sliding window.
+func (s *Server) rateLimitAuth(rl *ipRateLimiter, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ip := extractIP(r)
+		if !rl.Allow(ip) {
+			writeErr(w, http.StatusTooManyRequests, "terlalu banyak percobaan, coba lagi nanti")
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}