Deploy: drop cpus: limits and stop assuming docker compose exists

Two NAS realities, both hit on a real Synology box.

- "NanoCPUs" error part-way through the project build: `cpus:` maps to the
  NanoCPUs field, which DSM's Docker daemon rejects. Removed from all three
  services (and from .env.prod.example). mem_limit uses the much older Memory
  field and works, so memory caps remain the throttle. Noted in the header
  next to the other DSM constraints.
- `docker compose build` on DSM: "'compose' is not a docker command". DSM and
  QTS ship the standalone `docker-compose` binary with no plugin subcommand,
  so every one of the script's 21 compose invocations was wrong for the target
  platform. The script now detects which is present, and only passes `--wait`
  when it finds v2 — on v1 it falls back to the health_gate it already had,
  which is also now run after `up` on both paths.

That the build reached container creation before failing says their compose
parses the rest of the file (anchors, profiles, service_completed_successfully,
top-level name), so this was a daemon-level rejection, not a schema one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nux3LCu4zP9nih4BRhPyHw

docker-compose.yml

@@ -21,6 +21,10 @@
 #   Start:  ./deploy/webmail.sh up
 #   Manual: docker compose up -d          (reads .env from this directory)
 #
+#   Likewise, no `cpus:` limits: that maps to NanoCPUs, which DSM's Docker
+#   daemon rejects ("NanoCPUs can not be set"). mem_limit uses the much older
+#   Memory field and works fine, so memory caps are the throttle here.
+#
 #   Interpolation here must stay on the oldest, dumbest forms: ${VAR} and
 #   ${VAR:-default}. DSM's bundled Compose rejects `${VAR:?message}` with
 #   "invalid interpolation format", and rejects `include:` outright. Required
@@ -224,7 +228,6 @@ services:
       migrate: { condition: service_completed_successfully }
     restart: unless-stopped
     mem_limit: ${API_MEM_LIMIT:-512m}
-    cpus: ${API_CPUS:-1.0}
     logging: *logging
 
   worker-sync:
@@ -243,7 +246,6 @@ services:
       migrate: { condition: service_completed_successfully }
     restart: unless-stopped
     mem_limit: ${WORKER_SYNC_MEM_LIMIT:-512m}
-    cpus: ${WORKER_CPUS:-1.5}
     # Leases are released on SIGTERM (workers/run.py targets <10 s); give it room.
     stop_grace_period: 30s
     logging: *logging
@@ -262,7 +264,6 @@ services:
       migrate: { condition: service_completed_successfully }
     restart: unless-stopped
     mem_limit: ${WORKER_JOBS_MEM_LIMIT:-640m}
-    cpus: ${WORKER_CPUS:-1.5}
     stop_grace_period: 30s
     logging: *logging