Add prefix/suffix support, short ID fallback, unit docs

- config: add Prefix/Suffix fields to Config struct
- systemd: ServiceName/Generate/UnitPath/Install/Uninstall/Enable/Disable/Status all accept prefix+suffix
- runtime: fall back to short container ID (12 chars) when container has no name
- cmd: active, status, install all thread prefix/suffix from config
- systemd/generator_test.go: updated all calls + added TestGenerate_WithPrefixSuffix
- docs/generated-units.md: full examples of every unit type + ordering + naming
- README: updated config docs, prefix/suffix section, link to docs/

README.md

@@ -76,6 +76,9 @@ oldthing   podman    hein    no        no          —                 container
 **Location:** `/etc/unitdore/units.yaml`
 
 ```yaml
+prefix: ""                   # optional: prepended to all service names, e.g. "prod-"
+suffix: ""                   # optional: appended to all service names, e.g. "-svc"
+
 units:
   - name: nginx
     runtime: podman          # podman | docker
@@ -94,7 +97,35 @@ units:
     enabled: true
 ```
 
-## Generated unit file (example)
+### Prefix and suffix
+
+Set `prefix` and/or `suffix` to namespace your service files:
+
+```yaml
+prefix: prod-
+suffix: ""
+```
+
+Generates: `unitdore-prod-nginx.service`, `unitdore-prod-myapp.service`, etc.
+Prefix/suffix apply to the **service file name only** — container names are unchanged.
+
+### Unnamed containers
+
+If a container has no name, `syncup` uses its short container ID (first 12 chars) as the unit name.
+You can rename it later with `unitdore edit`.
+
+## Generated unit files
+
+See **[docs/generated-units.md](docs/generated-units.md)** for full examples covering:
+- System units (root)
+- User units (rootless)
+- Docker vs Podman
+- Custom commands
+- Prefix/suffix naming
+- Startup ordering
+- Unnamed containers (short ID fallback)
+
+Quick example:
 
 ```ini
 # /etc/systemd/system/unitdore-nginx.service
@@ -115,8 +146,6 @@ RestartSec=5
 WantedBy=multi-user.target
 ```
 
-For user units (rootless containers), files go to `~/.config/systemd/user/` and target `default.target`.
-
 ## Flags
 
 ```