宜博 / h3livestream

Add admin-batch-gen.html and batch generation endpoints (T9)

POST /api/admin/batch-gen takes {characterId, garmentIds[],
refDanceVideoIds?[]}, expands to one job per garment (cross-producted
with refDanceVideoIds when given, else one random active dance-ref per
garment like the single-generate default), and submits each through
the same submitGeneration() helper the single POST /api/admin/generate
route now uses — so the M.7 dedupe cache (existing characterId+
garmentId combo) is honored per combo, not just per batch.
GET /api/admin/batch-gen/status?batchId= returns that batch's
generationJobs records for progress polling.

admin-batch-gen.html: pick one character, multiple garments, and
optionally pin specific reference dances; submits the batch, polls
status every 3s into a progress table, and lets failed rows be
retried individually via POST /api/admin/generate. Linked from the
other admin pages' nav.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>