feat(health)!: promote to v1.0.0 — configurable check timeout via NewHandlerWithConfig

Add Config struct and NewHandlerWithConfig(logger, cfg, checks...) constructor.
Config.CheckTimeout sets the per-request deadline for all health checks; zero
value defaults to 5 seconds. NewHandler remains unchanged as a backward-compatible
wrapper. API committed as stable.

health_test.go

@@ -167,6 +167,30 @@ func TestHandler_JSON_Shape(t *testing.T) {
 	}
 }
 
+func TestHandlerWithConfig_CustomTimeout(t *testing.T) {
+	// 200ms delay check with a 50ms timeout — should be reported as DOWN.
+	h := NewHandlerWithConfig(&noopLogger{}, Config{CheckTimeout: 50 * time.Millisecond},
+		&mockCheck{name: "slow", priority: LevelCritical, delay: 200 * time.Millisecond},
+	)
+	code, resp := doRequest(t, h)
+	if code != http.StatusServiceUnavailable {
+		t.Errorf("want 503, got %d", code)
+	}
+	if resp.Status != "DOWN" {
+		t.Errorf("want DOWN, got %s", resp.Status)
+	}
+}
+
+func TestHandlerWithConfig_ZeroTimeout_UsesDefault(t *testing.T) {
+	h := NewHandlerWithConfig(&noopLogger{}, Config{},
+		&mockCheck{name: "db", priority: LevelCritical},
+	)
+	code, resp := doRequest(t, h)
+	if code != http.StatusOK || resp.Status != "UP" {
+		t.Errorf("want 200 UP, got %d %s", code, resp.Status)
+	}
+}
+
 func TestHandler_ContextTimeout(t *testing.T) {
 	// Check that times out faster than the 5s global timeout when client cancels.
 	h := NewHandler(&noopLogger{},