Merge origin/main into cursor/digest-insight-assembler-cc18

Resolve add/add and content conflicts from PR1 (#103) squash on main
against PR1+PR2+PR3 on this branch. Prefer branch tip (assembler,
per-recipient delivery, per-user cron, seed/admin endpoints, EMAIL
guard) since #103 tree matched 7b4dea1 and PR2/PR3 supersede it.

Author: venkateshsakamuri-lab