Clarify recording start and documented finish times in Dataset Viewer
The shared drawing-finish label in filenames and the generic date / time columns can be mistaken for per-recording times. This change exposes five explicit timing columns near the front of both Dataset Viewer configurations: recording_start_local, recording_start_basis, documented_finish_date, documented_finish_time, and finish_label_scope.
The 163 available starts are copied from the existing Recording Timing v2 evidence by permanent record ID. Its 176 unknown starts remain blank; the other 492 indexed records are marked outside that snapshot. Prospective finish labels explicitly describe the complete drawing/group. Historical label scope remains unspecified. All original 29 field values, 831 recording IDs, filenames, media bytes, and download URLs are preserved. The Files list still displays the original filenames; README explains their finish-label meaning.
Validation: 95 repository tests; all 831 metadata rows; all 16 pinned Timing v2 input receipts; exact reconstruction of the historical Timing v1 metadata checksum. The local VideoFolder loader reads both 34-column configurations and matches every timing value, null and media-path join using empty placeholders with decoding disabled. This does not claim hosted Viewer cache readiness.
This updates the still-untagged v0.7.0 preparation and its file receipts; it introduces no extra release version. Historical manifests and tagged releases remain unchanged. This PR is an unmerged proposal for review. It does not merge, tag, change the DOI, or deploy the website.