Move from flat src/ to per-function directories:
- src/slack-bot/ — Slack Bolt Lambda handler
- src/weekly-post/ — Monday schedule + pay post
- src/roster-sync/ — Daily 3CX roster sync
- src/shared/ — Lambda Layer with schedule, blocks, three_cx_client
Each function has its own requirements.txt and CodeUri. Shared
modules are deployed as a SAM Layer (afterhours-shared) importable
as `from shared.X import Y`.