[ravediamond]

Builds on #142; only the last commit (feat(datasets): delete episodes from a local dataset) is new. Draft until #142 lands, then I'll rebase.

Problem

#142 lets you set bad takes aside by moving them into a new dataset. When a take is plainly unusable (arm out of frame, recording started too early), keeping a copy just leaves a dataset to clean up by hand later.

Approach

A "Delete episodes" button next to "Move episodes". It opens the same dialog (renamed EpisodesDialog, with a mode), without the name field and with a red button. The text says the episodes are removed for good and points to Move to keep a copy.

• POST /datasets/delete-episodes runs LeRobot's delete_episodes into a staging dir and swaps it in for the source, so a failure leaves the source untouched. The episodes left are renumbered.
• It shares the checks and the swap with move (_load_for_episode_edit, _swap_in_staged_copy): 409 while recording, 422 for empty or negative indices, 400 for out-of-range indices or deleting every episode.

If this is one button too many for the browser, I'm happy to drop it and keep only move.

Testing

• pytest: a real delete on a LeRobot-written dataset, invalid requests, a failure mid-delete that leaves the source untouched, the 409 while recording, request validation.
• vitest (delete mode of the dialog), eslint, npm run build, pre-commit run --all-files.
• Drove both dialogs end to end in headless Chromium on a small recorded video dataset: the deleted episode is gone, the rest renumbered with their own frames, no staging dir left behind.

Tested on Linux (Jetson Orin, aarch64) only. Not tested on macOS, Windows, or a real SO-101 dataset.