feat(demo): add Demo Guide (8-step guided tour) and scenario overview

Adds a compact "Probeer een demonstratiescenario" page listing the 5 named
scenarios with live readiness from the manifest, plus a Demo Guide side
panel (bottom sheet on mobile) that walks an Operations Manager through
all 8 steps with per-step context, live-resolved routes, sessionStorage
progress, and a "Demo opnieuw voorbereiden" restart. Login's guided-demo
CTA now actually opens the guide. Fixes a real mobile topbar overflow the
new guide trigger introduced.

PROJECT_STATE.md

@@ -593,3 +593,41 @@ scenarios, demo manifest, About page). Gap audit: `docs/demo-release/current-dem
   server demo-ready.
 - Exact next action: Demo Guide (collapsible panel, 8 steps) + scenario overview (5 cards
   on the dashboard, consuming `/api/v1/demo/manifest`'s `scenarios` array) — task #31.
+
+### Batch 3 — Demo Guide + scenario overview (complete)
+
+- New `/scenarios` page (`Scenarios.tsx`): all 5 named scenarios as cards (title,
+  operational problem, duration, required role(s), "toont aan", ready/blocked status
+  from the manifest, "Start scenario" linking to the live `start_path`). Dashboard gets
+  one compact "Probeer een demonstratiescenario" panel (not 5 more cards — keeps the
+  existing dashboard uncluttered per the brief) showing readiness count and, for
+  Operations Managers, a guide resume/start control.
+- New Demo Guide: `DemoGuideContext` (sessionStorage-persisted `currentIndex`/`completed`
+  set — browser-only, never touches auth or business logic), 8 static steps
+  (`data/demoGuideSteps.ts`) each with what-you'll-see/why/start-action/expected-outcome,
+  resolving live routes from the manifest for the two scenario-backed steps (return,
+  duplicate-merge) so they can't drift from actual records. `DemoGuide.tsx` renders a
+  fixed side panel (desktop) that becomes a bottom sheet at ≤700px via CSS only (no
+  layout duplication); `DemoGuideTrigger` (topbar, Operations-Manager-only — the 8 steps
+  require OM throughout) shows a live `completed/8` pill. "Demo opnieuw voorbereiden"
+  calls the real reset endpoint, resets guide progress, and returns to `/login` (mirrors
+  the existing sidebar reset flow). Login's "Start begeleide demo" logs in as OM and
+  passes a one-shot `?guide=start` marker the dashboard consumes once then strips.
+- Fixed a real regression caught by the responsive-overflow tests: the new topbar guide
+  trigger pushed `.topbar-meta` past the viewport at ≤420px; fixed by hiding the guide
+  trigger (icon+pill) at that breakpoint — the Dashboard's own "Start demo-gids" control
+  remains reachable there. Also fixed a genuine mobile overflow in the new
+  `.demo-start-panel` (flex items without `min-width:0`/wrap on narrow screens).
+- Fixed one fragile new test (asserted on the transient `?guide=start` URL param, which
+  the app intentionally strips immediately — changed to assert the guide's actual open
+  state instead) and two Playwright strict-mode ambiguous-match errors; confirmed the
+  full 41+6=47-test suite passes twice in a row after these fixes (ruling out flakiness).
+- Evidence: frontend `tsc -b` clean, `npm run build` clean; full Playwright suite
+  **47 passed** (41 existing + 6 new `demo-guide.spec.ts`: scenario overview shows 5
+  ready cards after reset, starting a scenario navigates to its fixed record, guide
+  step navigation/jump/close, progress persists across page navigation, guide hidden
+  from Rental Employee, restart-from-guide resets data and returns to login). Backend
+  untouched this batch (no re-run needed; last backend gate was 127 passed/ruff/mypy
+  clean in Batch 2).
+- 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.