feat: podman-compose stack units and root/user execution scopes

- syncup: podman first, docker only as fallback (podman wins on name clash;
  existing docker units found in podman switch to podman)
- syncup: group podman-compose containers into one `kind: stack` unit per
  project (project, working_dir, compose_files, compose_bin from labels);
  disable existing member units ("part of stack <project>")
- generator: compose mode (podman-compose up/stop, WorkingDirectory) with
  pod start/stop fallback when compose binary/dir/files are missing
- reconcile: stacks disabled with "stack not found" when neither compose
  files nor pod exist
- root: scan root + rootless users listed in `users:` (podman only)
- non-root: config ~/.config/unitdore/units.yaml, own user units only
- sysuser package: runuser with XDG_RUNTIME_DIR/DBUS env, home/linger lookup
- install: warn when linger is not enabled for user units
- testdata/stack: podman-compose test stack and captured podman ps fixture
- docs: README, generated-units, man page, AGENTS, PLAN

PLAN.md

@@ -27,7 +27,8 @@ Think of it as: **config → systemd units → running services.**
 ## Non-Goals
 
 - Not a container runtime (doesn't replace Podman/Docker)
-- Not Kubernetes / Compose / Quadlet
+- Not Kubernetes / Quadlet
+- Compose: only wraps existing podman-compose stacks (one unit per project); docker compose planned
 - Not a daemon — runs on demand
 
 ---
@@ -172,6 +173,8 @@ unitdore/
 | 5 | Reconcile (auto-disable missing units) in syncup |
 | 6 | User unit support (rootless containers) |
 | 7 | Polish: `edit`, error handling, --dry-run flag |
+| 8 | podman-compose stacks (compose + pod fallback), root/user scopes |
+| 9 | docker compose stacks (`com.docker.compose.*` labels) |
 
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