feat(planner): upgrade POI discovery with unified modern component

PROBLEM:
User feedback: "on cherche quoi ? A quelle endroit ? Comment ? Quand ?"
POI search lacked clarity about search parameters (what/where/when/how).
MobilePoiTray was too basic (simple list, no images, minimal UX).

SOLUTION:
Created POIDiscoveryPanel - unified component merging:
- Modern visual design from POICardsPanel (Dashboard component)
- Advanced AI logic from useMobilePoiDiscovery composable

FEATURES:
✨ Contextual header
  - Eyebrow badge: "Autour de [Anchor stage]"
  - Title: "Découvrez des lieux uniques"
  - Counter: X suggestions IA
  - Timestamp: "Il y a X min"
  - Actions: Change anchor, refresh

✨ Visual filters
  - 8 category chips (viewpoint, activity, restaurant, museum, park, hotel, cafe, beach)
  - Interactive states (inactive/active with hover effects)
  - Material icons + labels
  - Radius slider (5-120 km) with dynamic label

✨ Modern card grid
  - Responsive grid (auto-fill 300px)
  - Cover images or icon placeholders
  - Overlay actions (add, preview) on hover
  - AI uniqueness badge (/100 score)
  - Category chip + title
  - Description (2-line ellipsis)
  - Meta chips (distance, rating, duration)
  - Tags (max 3)

✨ Animations
  - Hover: translateY(-6px) + shadow boost
  - Image zoom (scale 1.08)
  - Overlay fade-in with bounce

✨ States
  - Loading: 6 skeleton cards
  - Empty: Icon + message + refresh button
  - Success: Grid of suggestions

DESIGN:
- Glass morphism (backdrop-blur + color-mix)
- Responsive (300px desktop → 280px tablet → 1fr mobile)
- Dark theme compatible (CSS variables)
- Border radius: 14-16px
- Spacing: 18-20px gaps

INTEGRATION:
- Replaced MobilePoiTray in PlannerPage.web.vue POI tab
- Replaced MobilePoiTray in PlannerPage.mobile.vue POI tab & dialog
- Fixed prop names: categories → selected-categories
- Fixed event names: @update-radius → @update:radius-km (v-model syntax)
- Updated imports in both pages

TECHNICAL:
- Component: apps/web/src/modules/planner/components/POIDiscoveryPanel.vue
- Props: suggestions, loading, anchorLabel, lastUpdatedLabel, selectedCategories, availableCategories, radiusKm
- Events: refresh, add, preview, toggle-category, update:radiusKm, cycle-anchor
- Methods: getCategoryIcon, formatCategory, formatDistance, formatDuration
- Styles: SCSS scoped with deep targeting for Quasar components

FILES CHANGED:
- NEW: apps/web/src/modules/planner/components/POIDiscoveryPanel.vue (660 lines)
- MOD: apps/web/src/modules/planner/pages/PlannerPage.web.vue (replaced MobilePoiTray)
- MOD: apps/web/src/modules/planner/pages/PlannerPage.mobile.vue (replaced MobilePoiTray)

TESTS:
✅ pnpm type-check (PASS)
✅ pnpm build (PASS - 1m17s)

BENEFITS:
✅ Clear search context (what/where/when explicitly displayed)
✅ Modern visual appeal (images, glass morphism, animations)
✅ Better interactivity (hover states, quick actions)
✅ AI feedback (uniqueness badges, relevance scores)
✅ 1 component instead of 2 (MobilePoiTray + POICardsPanel partial merge)
✅ Responsive across all breakpoints

NOTES:
- MobilePoiTray.vue can now be removed (no longer used)
- POICardsPanel.vue remains on Dashboard (different use case)
- useMobilePoiDiscovery composable unchanged (reusable logic)
- Future: Add real images API, favorites system, advanced filters

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Technical breakdown:
- User request: "retravailler le composent de recherche des POIS"
- Merged POICardsPanel visual design + MobilePoiTray search logic
- Answers user's questions: "on cherche quoi ? où ? comment ? quand ?"
- Category filters → What
- Anchor label + radius → Where
- AI suggestions + filters → How
- Timestamp label → When