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.

compose.yaml

@@ -92,11 +92,13 @@ services:
     tmpfs:
       - /tmp
 
-  # mail-sync: pull M365 (and OnlyOffice/Gmail) mail every 10 s into the shared
-  # var volume, then rebuild the brain index. Runs on the index image so it can
-  # convert + index in-process. Needs ~/.config/brain/m365.env for the M365
-  # source; override MAIL_SYNC_SRC / MAIL_SYNC_ENV for other providers.
+  # mail-sync ETL: sync → import every 300s into shared var. Full brain rebuild
+  # only when MAIL_SYNC_INDEX=1 (expensive on large mail corpora). Default
+  # sources: onlyoffice,gmail. For M365 set MAIL_SYNC_SRC=m365 and put
+  # M365_TENANT/CLIENT_ID/CLIENT_SECRET/USERS in ~/.config/brain/mail.env
+  # (or m365.env + MAIL_SYNC_ENV). Gmail OAuth: mount ~/.gmail-mcp.
   #   docker compose up -d mail-sync
+  #   bin/stack/start-mail-sync
   mail-sync:
     image: ghcr.io/eslider/2dph:index
     build:
@@ -106,13 +108,16 @@ services:
     environment:
       HF_HOME: /data/hf
       KB_PY: python3
-      MAIL_SYNC_SRC: m365
-      MAIL_SYNC_ENV: /secret/m365.env
+      MAIL_SYNC_SRC: onlyoffice,gmail
+      MAIL_SYNC_ENV: /secret/mail.env
+      MAIL_SYNC_INDEX: "0"
+      HOME: /home/2dph
     volumes:
       - kb-model:/data/hf
       - kb-var:/app/var
       - ~/.config/brain:/secret:ro
-    command: ["mail-sync", "10"]
+      - ~/.gmail-mcp:/home/2dph/.gmail-mcp:ro
+    command: ["mail-sync", "300"]
     read_only: true
     tmpfs:
       - /tmp