- mam-api: add GET /api/v1/assets/:id/video streaming proxy that fetches
from RustFS/S3 and pipes to browser with range-request support, bypassing
direct S3 access from Chrome
- mam-api: fix /stream route to return /video proxy URL for both proxy and
original-mp4 assets; return null cleanly for non-playable sources
- s3/client: set requestChecksumCalculation/responseChecksumValidation to
WHEN_REQUIRED to suppress x-amz-checksum-mode header on signed URLs
- editor: fix loadSourceAsset to set state.sourceAsset even when no proxy
exists (info toast instead of bail-out) so Insert/Overwrite still work
- editor: add drag-and-drop from media panel to timeline — items are now
draggable, timeline container accepts drops and calls Timeline.addClip
with the asset at playhead position
- editor: add tl-drag-over CSS highlight on timeline during drag
