feat: production hardening — slog, rate limiting, integration tests, seed data (Phase 4)

- Structured logging: replace log.* with log/slog JSON output across backend
- Request logger middleware: logs method, path, status, duration for all non-health requests
- Rate limiting: token bucket (5 req/min, burst 10) on AI endpoints (/api/ai/*)
- Integration tests: full critical path test (auth -> create case -> add deadline -> dashboard)
- Seed demo data: 1 tenant, 5 cases with deadlines/appointments/parties/events
- docker-compose.yml: add all required env vars (DATABASE_URL, SUPABASE_*, ANTHROPIC_API_KEY)
- .env.example: document all env vars including DATABASE_URL and CalDAV note

backend/internal/middleware/ratelimit_test.go

@@ -0,0 +1,70 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestTokenBucket_AllowsBurst(t *testing.T) {
+	tb := NewTokenBucket(1.0, 5) // 1/sec, burst 5
+
+	handler := tb.LimitFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+
+	// Should allow burst of 5 requests
+	for i := 0; i < 5; i++ {
+		req := httptest.NewRequest("GET", "/test", nil)
+		w := httptest.NewRecorder()
+		handler.ServeHTTP(w, req)
+		if w.Code != http.StatusOK {
+			t.Fatalf("request %d: expected 200, got %d", i+1, w.Code)
+		}
+	}
+
+	// 6th request should be rate limited
+	req := httptest.NewRequest("GET", "/test", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+	if w.Code != http.StatusTooManyRequests {
+		t.Fatalf("request 6: expected 429, got %d", w.Code)
+	}
+}
+
+func TestTokenBucket_DifferentIPs(t *testing.T) {
+	tb := NewTokenBucket(1.0, 2) // 1/sec, burst 2
+
+	handler := tb.LimitFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	})
+
+	// Exhaust IP1's bucket
+	for i := 0; i < 2; i++ {
+		req := httptest.NewRequest("GET", "/test", nil)
+		req.Header.Set("X-Forwarded-For", "1.2.3.4")
+		w := httptest.NewRecorder()
+		handler.ServeHTTP(w, req)
+		if w.Code != http.StatusOK {
+			t.Fatalf("ip1 request %d: expected 200, got %d", i+1, w.Code)
+		}
+	}
+
+	// IP1 should now be limited
+	req := httptest.NewRequest("GET", "/test", nil)
+	req.Header.Set("X-Forwarded-For", "1.2.3.4")
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+	if w.Code != http.StatusTooManyRequests {
+		t.Fatalf("ip1 request 3: expected 429, got %d", w.Code)
+	}
+
+	// IP2 should still work
+	req = httptest.NewRequest("GET", "/test", nil)
+	req.Header.Set("X-Forwarded-For", "5.6.7.8")
+	w = httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+	if w.Code != http.StatusOK {
+		t.Fatalf("ip2 request 1: expected 200, got %d", w.Code)
+	}
+}