* feat(mail): add Microsoft 365 Graph sync source with delta state
Adds a GET-only Microsoft Graph source to bin/mail/sync (client-credentials,
delta query). Wires it into the CLI (--source m365), the worker pool and the
compose stack:
- m365.go: M365Client (token cache, delta pagination, message normalization,
attachment download) + m365Source adapter (per-mailbox folders + delta link)
- sync.go: M365Credentials in SyncConfig; Committer interface so delta links
only advance after a fully successful run (no skips on failure)
- cli.go: --source m365 with M365_/MS_ env passthrough
- Dockerfile: mail-build stage produces /mail-sync into the index image
- docker-entrypoint: mail-sync loop (sync -> import -> index, default 10s)
- compose.yaml: mail-sync service (index image, kb-var volume, secrets ro)
* feat(mail): adapt M365 ETL loop for OO+Gmail bots.
Default compose mail-sync to onlyoffice,gmail every 300s with import on new
mail; gate full --rebuild behind MAIL_SYNC_INDEX. Fix mail-build stage order
and add bin/stack/start-mail-sync.
