refactor(monitoring): simplify brand dashboard and harden citation rendering

- drop brand_time_buckets and sparkline/coverage UI; dashboard now returns a single day
- compute mention rate from total actual samples instead of averaging per-platform rates
- canonicalize ai_platform_id across services and aggregate platform-overview snapshots
- strip mojibake and non-answer noise from callback payloads and question detail answers
- keep Kimi citations panel-only; still store raw search_results for audit
- render linked [n] inline citations for qwen/yuanbao answers with scroll-to-source behavior
- restrict立即采集 to today's business date with a clear i18n hint
- refresh content-citations into an ant-design table with truncation and hover styling

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/internal/tenant/app/monitoring_text_encoding_test.go

@@ -0,0 +1,21 @@
+package app
+
+import "testing"
+
+func TestRepairMonitoringMojibake(t *testing.T) {
+	input := "用户询问合肥全屋定制的性价比最高的品牌"
+	got := repairMonitoringMojibake(input)
+	want := "用户询问合肥全屋定制的性价比最高的品牌"
+
+	if got != want {
+		t.Fatalf("repairMonitoringMojibake() = %q, want %q", got, want)
+	}
+}
+
+func TestRepairMonitoringMojibakeLeavesNormalChineseUntouched(t *testing.T) {
+	input := "用户询问合肥全屋定制的性价比最高的品牌"
+	got := repairMonitoringMojibake(input)
+	if got != input {
+		t.Fatalf("repairMonitoringMojibake() changed valid text: got %q, want %q", got, input)
+	}
+}