[shots] Add bulk shot generation to the Create shots modal

[mxatmx]

Add a "Bulk" tab to the Create shots modal that generates a range of shot names from a start name, count and step (e.g. SH010, SH020, ...), previews them, and creates them in one pass via the existing CSV import. Adds a generateBulkShotNames string helper and a bulkCreateShots store action.

[frankrousseau]

Please don't use callback. Use only promises.

[frankrousseau]

Two small guards worth adding to the bulk tab:

1. TV show with no episode selected → empty Episode cell in the CSV. isBulkGenerateAllowed only requires selectedSequenceId; on a TV show with selectedEpisodeId null, episodeName ?? null ends up as "" in the generated CSV and the result depends on how zou handles an empty episode column. Adding (!isTVShow || selectedEpisodeId) to the condition closes it.

2. Negative step is not blocked. min="1" on the input doesn't prevent typing -10, and the !bulk.step guard only catches 0. Result: preview names like SH-10, SH-20, creatable if there is no collision. A bulk.step < 1 check in the bulkPreviewNames guard is enough.

Minor, non-blocking: on import failure the modal only does console.error + spinner reset — with up to 500 shots at stake, surfacing an error message in the modal would help.