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>

backend/app/domains/media/router.py

@@ -1,17 +1,18 @@
 """MediaAsset router — /api/media."""
 import io
+import math
 import uuid
 import zipfile
 
 from fastapi import APIRouter, Depends, HTTPException, Query
 from fastapi.responses import StreamingResponse
-from sqlalchemy import select
+from sqlalchemy import select, func
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import get_db
 from app.domains.auth.models import User
 from app.domains.media.models import MediaAsset, MediaAssetType
-from app.domains.media.schemas import MediaAssetOut
+from app.domains.media.schemas import MediaAssetOut, MediaAssetBrowseItem, MediaAssetBrowseResponse
 from app.domains.media import service
 from app.utils.auth import get_current_user
 
@@ -98,6 +99,109 @@ async def list_assets(
     return assets
 
 
+@router.get("/assets", response_model=MediaAssetBrowseResponse)
+async def browse_media_assets(
+    asset_type: str | None = None,
+    category_key: str | None = None,
+    render_status: str | None = None,
+    q: str | None = None,
+    page: int = Query(1, ge=1),
+    page_size: int = Query(50, ge=1, le=200),
+    _user: User = Depends(get_current_user),
+    db: AsyncSession = Depends(get_db),
+) -> MediaAssetBrowseResponse:
+    """Media browser: server-side filtered + paginated asset list with product context."""
+    from app.domains.products.models import Product
+    from app.domains.orders.models import OrderLine
+    from sqlalchemy import desc
+
+    # Build query with LEFT JOINs to get product and order_line context.
+    # MediaAsset has direct product_id FK and order_line_id FK.
+    # OrderLine has render_status which we also want to surface.
+    stmt = (
+        select(
+            MediaAsset,
+            Product.name.label("product_name"),
+            Product.pim_id.label("product_pim_id"),
+            Product.category_key.label("category_key"),
+            OrderLine.render_status.label("render_status"),
+        )
+        .outerjoin(Product, MediaAsset.product_id == Product.id)
+        .outerjoin(OrderLine, MediaAsset.order_line_id == OrderLine.id)
+        .where(MediaAsset.is_archived == False)  # noqa: E712
+        .order_by(desc(MediaAsset.created_at))
+    )
+
+    # Apply filters
+    if asset_type:
+        try:
+            at_enum = MediaAssetType(asset_type)
+            stmt = stmt.where(MediaAsset.asset_type == at_enum)
+        except ValueError:
+            pass  # invalid type → ignore filter
+
+    if category_key:
+        stmt = stmt.where(Product.category_key == category_key)
+
+    if render_status:
+        stmt = stmt.where(OrderLine.render_status == render_status)
+
+    if q:
+        pattern = f"%{q}%"
+        from sqlalchemy import or_
+        stmt = stmt.where(
+            or_(
+                Product.name.ilike(pattern),
+                Product.pim_id.ilike(pattern),
+            )
+        )
+
+    # Count total matching rows
+    count_stmt = select(func.count()).select_from(stmt.subquery())
+    total_result = await db.execute(count_stmt)
+    total = total_result.scalar_one()
+
+    # Paginate
+    offset = (page - 1) * page_size
+    stmt = stmt.offset(offset).limit(page_size)
+
+    rows = await db.execute(stmt)
+    items: list[MediaAssetBrowseItem] = []
+    for row in rows.all():
+        asset: MediaAsset = row[0]
+        product_name: str | None = row[1]
+        product_pim_id: str | None = row[2]
+        cat_key: str | None = row[3]
+        r_status: str | None = row[4]
+
+        item = MediaAssetBrowseItem(
+            id=asset.id,
+            asset_type=asset.asset_type,
+            file_path=asset.storage_key,
+            file_size_bytes=asset.file_size_bytes,
+            mime_type=asset.mime_type,
+            created_at=asset.created_at,
+            order_line_id=asset.order_line_id,
+            product_id=asset.product_id,
+            product_name=product_name,
+            product_pim_id=product_pim_id,
+            category_key=cat_key,
+            render_status=r_status,
+            download_url=f"/api/media/{asset.id}/download",
+            thumbnail_url=service.get_thumbnail_url(asset),
+        )
+        items.append(item)
+
+    pages = max(1, math.ceil(total / page_size))
+    return MediaAssetBrowseResponse(
+        items=items,
+        total=total,
+        page=page,
+        page_size=page_size,
+        pages=pages,
+    )
+
+
 @router.get("/{asset_id}", response_model=MediaAssetOut)
 async def get_asset(asset_id: uuid.UUID, db: AsyncSession = Depends(get_db)):
     asset = await service.get_media_asset(db, asset_id)