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/pages/DataQualityIssueDetail.tsx

@@ -15,6 +15,8 @@ import { useDemoGuide } from "../context/DemoGuideContext";
 import { useDemoManifest } from "../context/DemoManifestContext";
 import { useLocaleFormat } from "../i18n/format";
 import { DEMO_GUIDE_STEPS } from "../data/demoGuideSteps";
+import { describeEvidenceSignal } from "../data/evidenceSignals";
+import type { EvidenceSignal } from "../api/types";
 import { Icon } from "../components/Icons";
 import { ApiErrorNotice, ErrorState, LoadingState, PageHeader, SectionHeading } from "../components/PageChrome";
 
@@ -47,74 +49,21 @@ function EvidenceDisclosure({ issue }: { issue: IssueDetail }) {
   );
 }
 
-interface EvidenceSignal {
-  code: string;
-  params?: Record<string, unknown>;
-}
-
 // The backend never emits prose for evidence -- only stable signal codes + raw data
-// params (see app/services/data_quality.py::_open_issue). This is the one place that
-// turns them into the operator's selected language; the legacy `evidence.summary`
-// string is a technical fallback only, shown solely inside EvidenceDisclosure above.
-// A handful of seed-only rows (generic filler, not tied to a scripted demo scenario)
-// carry no structured signals -- rather than show nothing, this known placeholder
-// summary gets a localized rendering. Any other un-signalled legacy text still falls
-// back to the raw string (better than a blank primary evidence area), but only
-// "Technical details" is meant to guarantee raw-text visibility.
-const SEED_PLACEHOLDER_SUMMARY = "Synthetic deterministic seed issue";
-
+// params (see app/services/data_quality.py::_open_issue). describeEvidenceSignal is the
+// one place that turns them into the operator's selected language; the legacy
+// `evidence.summary` string is a technical fallback only, shown solely inside
+// EvidenceDisclosure above.
 function EvidenceSignalList({ issue }: { issue: IssueDetail }) {
   const { t } = useTranslation("quality");
   const { formatNumber } = useLocaleFormat();
   const signals = (issue.evidence.signals as EvidenceSignal[] | undefined) ?? [];
-  if (signals.length === 0) {
-    const rawSummary = String(issue.evidence.summary ?? "");
-    if (!rawSummary) return null;
-    const text =
-      rawSummary === SEED_PLACEHOLDER_SUMMARY
-        ? t("detail.evidence.seedPlaceholder")
-        : rawSummary;
-    return (
-      <ul className="evidence-signal-list">
-        <li>{text}</li>
-      </ul>
-    );
-  }
-
-  function describe(signal: EvidenceSignal): string {
-    const { code, params = {} } = signal;
-    if (code.startsWith("vehicle.")) {
-      return t(`detail.vehicleStatusConflict.reasonCodes.${code}`, { defaultValue: code });
-    }
-    switch (code) {
-      case "missing_field":
-        return t("detail.evidence.missingField", {
-          field: t(`detail.missingField.fields.${params.field}`, { defaultValue: String(params.field) }),
-        });
-      case "overlap.reserved_bookings":
-        return t("detail.evidence.overlapReservedBookings", {
-          refs: Array.isArray(params.refs) ? params.refs.join(" ↔ ") : "",
-        });
-      case "odometer.regression":
-        return t("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("detail.evidence.duplicateSimilarName", { score: params.score });
-      case "attention.upcoming_booking_missing_inspection":
-        return t("detail.evidence.upcomingBookingMissingInspection", { bookingRef: params.booking_ref });
-      default:
-        return t(`detail.evidence.${code}`, { defaultValue: code });
-    }
-  }
+  if (signals.length === 0) return null;
 
   return (
     <ul className="evidence-signal-list">
       {signals.map((signal, index) => (
-        <li key={`${signal.code}-${index}`}>{describe(signal)}</li>
+        <li key={`${signal.code}-${index}`}>{describeEvidenceSignal(t, formatNumber, signal)}</li>
       ))}
     </ul>
   );