The `000016_task_template_id` and `000017_drop_task_template_regions_join`
migrations introduced on gitea collided with the existing unpadded 016/017
migrations (authtoken_created_at, fk_indexes). Renamed them to 021/022 so
they extend the shipped sequence instead of replacing real migrations.
Also removed the padded 000012-000015 files which were duplicate content
of the shipped 012-015 unpadded migrations.
Dockerfile builder image bumped from golang:1.24-alpine to 1.25-alpine to
match go.mod's `go 1.25` directive.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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