feat: asset-based image/video sources, notification sounds, UI improvements

- Replace URL-based image_source/url fields with image_asset_id/video_asset_id
  on StaticImagePictureSource and VideoCaptureSource (clean break, no migration)
- Resolve asset IDs to file paths at runtime via AssetStore.get_file_path()
- Add EntitySelect asset pickers for image/video in stream editor modal
- Add notification sound configuration (global sound + per-app overrides)
- Unify per-app color and sound overrides into single "Per-App Overrides" section
- Persist notification history between server restarts
- Add asset management system (upload, edit, delete, soft-delete)
- Replace emoji buttons with SVG icons throughout UI
- Various backend improvements: SQLite stores, auth, backup, MQTT, webhooks

server/tests/e2e/test_backup_flow.py

@@ -1,9 +1,11 @@
 """E2E: Backup and restore flow.
 
-Tests creating entities, backing up (SQLite .db file), deleting, then restoring.
+Tests creating entities, backing up (ZIP containing SQLite .db + asset files),
+deleting, then restoring.
 """
 
 import io
+import zipfile
 
 
 class TestBackupRestoreFlow:
@@ -40,12 +42,17 @@ class TestBackupRestoreFlow:
         resp = client.get("/api/v1/color-strip-sources")
         assert resp.json()["count"] == 1
 
-        # 2. Create a backup (GET returns a SQLite .db file)
+        # 2. Create a backup (GET returns a ZIP containing ledgrab.db + assets)
         resp = client.get("/api/v1/system/backup")
         assert resp.status_code == 200
         backup_bytes = resp.content
-        # SQLite files start with this magic header
-        assert backup_bytes[:16].startswith(b"SQLite format 3")
+        # Backup is a ZIP file (PK magic bytes)
+        assert backup_bytes[:4] == b"PK\x03\x04"
+        # ZIP should contain ledgrab.db
+        with zipfile.ZipFile(io.BytesIO(backup_bytes)) as zf:
+            assert "ledgrab.db" in zf.namelist()
+            db_data = zf.read("ledgrab.db")
+            assert db_data[:16].startswith(b"SQLite format 3")
 
         # 3. Delete all created entities
         resp = client.delete(f"/api/v1/color-strip-sources/{css_id}")
@@ -59,23 +66,27 @@ class TestBackupRestoreFlow:
         resp = client.get("/api/v1/color-strip-sources")
         assert resp.json()["count"] == 0
 
-        # 4. Restore from backup (POST with the .db file upload)
+        # 4. Restore from backup (POST with the .zip file upload)
         resp = client.post(
             "/api/v1/system/restore",
-            files={"file": ("backup.db", io.BytesIO(backup_bytes), "application/octet-stream")},
+            files={"file": ("backup.zip", io.BytesIO(backup_bytes), "application/zip")},
         )
         assert resp.status_code == 200, f"Restore failed: {resp.text}"
         restore_result = resp.json()
         assert restore_result["status"] == "restored"
         assert restore_result["restart_scheduled"] is True
 
-    def test_backup_is_valid_sqlite(self, client):
-        """Backup response is a valid SQLite database file."""
+    def test_backup_is_valid_zip(self, client):
+        """Backup response is a valid ZIP containing a SQLite database."""
         resp = client.get("/api/v1/system/backup")
         assert resp.status_code == 200
-        assert resp.content[:16].startswith(b"SQLite format 3")
+        assert resp.content[:4] == b"PK\x03\x04"
         # Should have Content-Disposition header for download
         assert "attachment" in resp.headers.get("content-disposition", "")
+        # ZIP should contain ledgrab.db with valid SQLite header
+        with zipfile.ZipFile(io.BytesIO(resp.content)) as zf:
+            assert "ledgrab.db" in zf.namelist()
+            assert zf.read("ledgrab.db")[:16].startswith(b"SQLite format 3")
 
     def test_restore_rejects_invalid_format(self, client):
         """Uploading a non-SQLite file should fail validation."""