feat(phase7.2): media browser with server-side filters + pagination

- Migration 052: indexes on media_assets(asset_type, created_at) and
  products(category_key, lagertyp) for efficient filter queries
- GET /api/media/assets: JOINs media_assets→products→order_lines,
  filters by asset_type / category_key / render_status / q (ILIKE),
  paginated (page/page_size), returns total+pages count
- New schemas: MediaAssetBrowseItem, MediaAssetBrowseResponse
- frontend/src/api/media.ts: getMediaAssets(filters), typed interfaces
- MediaBrowser.tsx: rewritten with sticky filter bar (debounced search,
  type/category/status dropdowns), responsive grid, image previews,
  download buttons, pagination footer with page size selector
- Renamed legacy function to listMediaAssets for backward compat

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/cad/InlineCadViewer.tsx

@@ -6,7 +6,7 @@ import * as THREE from 'three'
 import { mergeVertices } from 'three/examples/jsm/utils/BufferGeometryUtils.js'
 import { Loader2, Box, RefreshCw, Grid3X3, Layers, Sun, Cpu } from 'lucide-react'
 import { toast } from 'sonner'
-import { getMediaAssets } from '../../api/media'
+import { listMediaAssets as getMediaAssets } from '../../api/media'
 import { generateGltfGeometry } from '../../api/cad'
 import { useAuthStore } from '../../store/auth'