fix: localize the primary data-quality evidence summary (live-caught on Unraid)

Live validation on the deployed fix branch caught a real bug: every data-quality
issue's top-of-page "Evidence summary" line rendered the raw, always-English legacy
evidence.summary string unconditionally -- in all three languages -- even though the
backend has been emitting structured, localizable evidence.signals for a while
(app/services/data_quality.py already documented this exact intent). The frontend
side of that conversion was never finished.

- DataQualityIssueDetail.tsx now renders evidence.signals through the operator's
  locale as the primary summary; the raw evidence.summary string is only visible
  inside "Technical details" (via the existing EvidenceDisclosure JSON dump).
- The four DQ-DEMO-* seed rows that anchor the guided demo's scripted scenarios now
  carry real, accurate signals computed at seed time (duplicate-customer's similarity
  score is the actual SequenceMatcher ratio on the seeded names, not invented) instead
  of only a legacy English sentence.
- Rows with no structured signals (generic filler seed data) fall back to the raw
  text rather than showing a blank summary; the one known placeholder string gets its
  own localized rendering so it never displays as English filler either.
- New regression test: the vehicle_status_conflict evidence summary must show
  localized text and must never contain the specific raw English sentence that was
  live-visible before this fix, in all 3 languages.

151 backend tests, Ruff, mypy green; full local Playwright suite green (a couple of
sequential-run-only flakes, both confirmed to pass in isolation and unrelated to this
change).

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

frontend/e2e/fleet-ops-correction.spec.ts

@@ -350,3 +350,30 @@ test.describe("route matrix (section 11F)", () => {
     });
   }
 });
+
+test.describe("data-quality evidence summary is localized, not raw English (section 6)", () => {
+  // The primary evidence line at the top of every issue's detail page must render the
+  // structured `evidence.signals` in the operator's language; the legacy English
+  // `evidence.summary` string is a technical fallback only, visible solely inside
+  // "Technical details". Live-caught: this line was unconditionally showing raw
+  // English ("vehicle marked available while reserved bookings conflict") in every
+  // language until fixed.
+  const cases: { lang: string; expectedText: RegExp }[] = [
+    { lang: "nl-BE", expectedText: /overlappende reserveringen/i },
+    { lang: "en-GB", expectedText: /overlapping bookings/i },
+    { lang: "fr-BE", expectedText: /chevauchent|chevauchement/i },
+  ];
+
+  for (const { lang, expectedText } of cases) {
+    test(`vehicle_status_conflict evidence is localized (${lang})`, async ({ page, request }) => {
+      await resetDemoData(request);
+      await loginAsOpsManager(page, lang);
+      await page.goto("/data-quality/DQ-DEMO-STATUS");
+
+      const summarySection = page.locator(".record-surface-evidence");
+      await expect(summarySection).toBeVisible();
+      await expect(summarySection).toContainText(expectedText);
+      await expect(summarySection).not.toContainText("vehicle marked available while reserved bookings conflict");
+    });
+  }
+});