fix: localize dashboard evidence, explain blocked vehicles, clarify pending odometers

Three content defects found by a live reviewer:

- Dashboard attention subtext was raw, untranslated evidence.summary text, and for
  11 of 15 seeded issues that text was literally "Synthetic deterministic seed
  issue". AttentionItem now exposes evidence_signals (stable code + params, same
  shape as the issue detail page) instead of a detail string; the frontend renders
  them through a shared describeEvidenceSignal() used by both the dashboard and the
  issue detail page. Every previously-placeholder seed row now cites a real,
  per-rule-type fact (a genuinely crossed service threshold, a genuinely blank
  field, or a real pair of booking odometer readings) instead of invented prose.

- 5 of 7 blocked vehicles had no quality issue at all and one had only a resolved
  one, so "needs attention" led nowhere. Each now has a real open
  missing_required_field issue backed by a genuinely blank field (no schema change,
  no migration -- reuses the existing data-quality pipeline).

- Booking odometer fields showing a bare "-" for 25 reserved + 1 active booking now
  show a localized explanation ("trip hasn't started yet" / "not yet closed").
  MO-024's rented-but-service-overdue contradiction was already caught by the
  vehicle-status evaluator (DQ-SCAN, vehicle.manual_review_required) -- added a
  regression test rather than new logic.

Also fixed a related bug the above exposed: the vehicle entity_snapshot omitted
registration_number entirely, so the "provide missing fields" form always showed
it blank regardless of the real value.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/data/evidenceSignals.ts

@@ -0,0 +1,42 @@
+import type { EvidenceSignal } from "../api/types";
+
+type TFunction = (key: string, options?: Record<string, unknown>) => string;
+
+// The backend never emits prose for data-quality evidence -- only stable signal codes
+// plus raw data params (see backend/app/services/data_quality.py::_open_issue). This is
+// the one place that turns them into the operator's selected language, shared by the
+// issue detail page and the dashboard attention queue so the same code always reads the
+// same way everywhere it appears.
+export function describeEvidenceSignal(
+  t: TFunction,
+  formatNumber: (value: number) => string,
+  signal: EvidenceSignal,
+): string {
+  const { code, params = {} } = signal;
+  if (code.startsWith("vehicle.")) {
+    return t(`quality:detail.vehicleStatusConflict.reasonCodes.${code}`, { defaultValue: code });
+  }
+  switch (code) {
+    case "missing_field":
+      return t("quality:detail.evidence.missingField", {
+        field: t(`quality:detail.missingField.fields.${params.field}`, { defaultValue: String(params.field) }),
+      });
+    case "overlap.reserved_bookings":
+      return t("quality:detail.evidence.overlapReservedBookings", {
+        refs: Array.isArray(params.refs) ? params.refs.join(" ↔ ") : "",
+      });
+    case "odometer.regression":
+      return t("quality:detail.evidence.odometerRegression", {
+        laterRef: params.later_ref,
+        laterKm: formatNumber(Number(params.later_km ?? 0)),
+        earlierRef: params.earlier_ref,
+        earlierKm: formatNumber(Number(params.earlier_km ?? 0)),
+      });
+    case "duplicate.similar_name":
+      return t("quality:detail.evidence.duplicateSimilarName", { score: params.score });
+    case "attention.upcoming_booking_missing_inspection":
+      return t("quality:detail.evidence.upcomingBookingMissingInspection", { bookingRef: params.booking_ref });
+    default:
+      return t(`quality:detail.evidence.${code}`, { defaultValue: code });
+  }
+}