feat(demo): make return, data-quality and knowledge flows demo-legible

Fixes a real honesty bug in Knowledge.tsx (body copy named "RAGcore" while
the active provider is the demo one) and a second real bug discovered
while fixing it: the brief's suggested Dutch questions would silently
return "insufficient evidence" against the English-only demo knowledge
base -- verified empirically and fixed by keeping suggested questions in
English. The return flow now pre-fills the odometer-regression scenario's
suspicious reading instead of asking a visitor to invent one, and links
to automation/audit after committing. Data-quality issues get a shared
plain-language "what's wrong / why it matters" explainer per rule type,
a post-resolution confirmation with audit/vehicle links, and a "demo
scenario's only" list filter. Also fixes a real async race where the
odometer pre-fill could clobber text a visitor had already started typing.

PROJECT_STATE.md

@@ -640,3 +640,47 @@ scenarios, demo manifest, About page). Gap audit: `docs/demo-release/current-dem
   the server demo-ready.
 - Exact next action: layer plain-language Dutch explanation onto the return flow, the 5
   data-quality panels, and fix the knowledge assistant's RAGcore-naming bug — task #33.
+
+### Batch 4 — return/data-quality/knowledge demo legibility (complete)
+
+- **Fixed a real honesty bug**: `Knowledge.tsx` named "RAGcore" in the body copy and the
+  retrieval-flow diagram even though the active provider is the demo TF-IDF one (the
+  small badge below was already honest, contradicting the prose one line above). Now
+  derives a `providerLabel` ("Demo knowledge base" vs "RAGcore") from the real health
+  check and uses it everywhere; added an explicit disclosure note when not RAGcore.
+  Added 4 suggested-question chips. **Discovered and fixed a second real bug in the
+  process**: the brief's suggested Dutch questions (and my own Demo Guide step 6 wording)
+  would have returned "insufficient evidence" against the demo provider, because the
+  indexed procedures are English-only — verified empirically (Dutch question →
+  `insufficient`, its English equivalent → `grounded`). Fixed by keeping suggested
+  questions in English (matching the indexed content) and rewording the Guide step to
+  explain the knowledge base is English, rather than mistranslating the demo's
+  centerpiece feature into silently returning wrong answers.
+- Return flow: `BookingDetail.tsx` now detects the one named return-anomaly scenario
+  booking (via the manifest, not a hardcoded ref) and fetches that vehicle's real
+  canonical odometer to pre-fill `ReturnForm`'s "End odometer" field with a suspicious
+  value below it, plus a callout explaining why — the brief explicitly requires the demo
+  not ask a visitor to invent a suspicious number themselves. Scoped narrowly to that one
+  scenario booking; ordinary returns are unaffected. `ReturnResultPanel` now links to
+  Automation and Audit trail (previously only the vehicle), and shows a "Ga verder met de
+  demo" button when the Demo Guide is open (advances the guide and navigates to the next
+  step). **Fixed a real regression caught by the existing return-review e2e test**: the
+  async pre-fill could silently overwrite odometer text a visitor had already started
+  typing, if the vehicle-detail fetch resolved after they began typing — fixed with an
+  `odometerEditedByUser` ref guard.
+- Data quality: added a shared `RuleExplainer` (what's wrong / why it matters, in plain
+  language) for all 5 rule types on `DataQualityIssueDetail.tsx`; added a generic
+  post-resolution confirmation (audit-trail link, vehicle link, "Ga verder met de demo")
+  for the 4 rule types that previously just silently flipped their status badge with no
+  explicit confirmation, and extended `VehicleStatusConflictPanel`'s existing confirmation
+  with the same links rather than duplicating it. Added a "Demo scenario's only" checkbox
+  filter on `DataQuality.tsx` (client-side `public_ref.startsWith("DQ-DEMO-")`, no new
+  business logic) so the curated issues are easy to find among the full queue.
+- Evidence: frontend `tsc -b` clean, `npm run build` clean; full Playwright suite
+  **51 passed** (47 existing + 4 new `demo-legibility.spec.ts`: return pre-fill + why-
+  suspicious explanation + result links, rule explainer visible, demo-scenario filter
+  narrows correctly, knowledge suggested question returns grounded evidence with the
+  correct provider label). Backend untouched this batch.
+- Exact next action: plain-language integration-status labels, richer audit narration,
+  the full "Over deze demo" page content (currently a first pass from Batch 2), and
+  wiring reset into the guide/About/OM menu narrative — task #34.