Drop the compose file and systemd unit for the sync server

The server is a single process, so a compose file that only wrapped one
container added a second way to do the same thing. Docker is now the one
documented path, pointing at a Postgres that lives outside the container.

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AGENTS.md

@@ -42,12 +42,11 @@ clicking an item copies it back to the clipboard.
   code and server URL in `UserDefaults` (`sync.code`, `sync.serverURL`,
   `sync.version`), pushes the whole store as JSON, and polls every 5s.
 - `Server/main.go` — the Go sync backend (single file, `net/http` + `lib/pq`).
-  Also ships `Server/Dockerfile` + `Server/docker-compose.yml` (Postgres +
-  server), `Server/README.md` (self-hosting), and `Server/prompt-sync.service`
-  (systemd unit). Logs one line per request, creates its schema on startup,
-  shuts down gracefully on SIGTERM so a redeploy cannot cut off a push, and
-  supports `-healthcheck` (pings local `/healthz`) so the distroless image
-  needs no shell for its Docker `HEALTHCHECK`.
+  Also ships `Server/Dockerfile` (static binary on distroless) and
+  `Server/README.md` (self-hosting). Logs one line per request, creates its
+  schema on startup, shuts down gracefully on SIGTERM so a redeploy cannot cut
+  off a push, and supports `-healthcheck` (pings local `/healthz`) so the
+  shell-less image needs no curl for its Docker `HEALTHCHECK`.
 
 ## Sync protocol