feat(ui): mobile responsiveness audit + type fixes

Mobile Responsiveness:
- Viewport meta tags toegevoegd in layout.tsx
- EPD header: patient details verborgen op mobiel, zoekbalk responsive
- Agenda: auto-switch naar dagview op mobiel, mini-kalender verborgen
- Agenda toolbar: verticale stacking, Week/Werkweek knoppen verborgen
- Patiëntenlijst: compact icoon-only button op mobiel
- Verpleegrapportage: verticale flow i.p.v. twee-koloms layout
- Cortex: artifact overlay met slide-in animatie op mobiel
- Cortex: "Terug" knop toegevoegd aan artifact panels
- Toast feedback bij succesvolle afspraak creatie

Code Quality Fixes (KISS/DRY):
- Resize listener vervangen door bestaande useMediaQuery hook
- Dubbele flex class opgeschoond in epd-header.tsx
- userScalable: false verwijderd (accessibility)

Type Fixes:
- actions.ts: status literal type met 'as const'
- agenda-block.tsx: dateRange start/end optioneel
- chat-empty-state.tsx: framer-motion ease type
- cortex-store.ts: ChatEntities.dateRange consistent met Zod schema

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

components/cortex/artifacts/blocks/agenda-block.tsx

@@ -36,7 +36,7 @@ export function AgendaBlock({
 }: AgendaBlockProps) {
     // State for fetched appointments (only used in list mode)
     const [appointments, setAppointments] = useState<CalendarEvent[] | undefined>(initialAppointments);
-    const [dateRange, setDateRange] = useState<{ start: Date; end: Date; label: string } | undefined>(initialDateRange);
+    const [dateRange, setDateRange] = useState<{ start?: Date; end?: Date; label: string } | undefined>(initialDateRange);
     const [isLoading, setIsLoading] = useState(false);
     const [error, setError] = useState<string | null>(null);
     const [refetchKey, setRefetchKey] = useState(0);