feat(install): auto-start the dashboard on boot via systemd, no Claude Code needed

Adds ccam service install/uninstall/status for checkout installs and wires
the same systemd --user unit into plugin-bootstrap.js, so plugin-installed
colleagues get boot persistence too instead of needing a Claude Code
session to (re)start the server after every reboot.

README.md

@@ -71,6 +71,27 @@ at its own runtime directory). `postinstall` writes the Claude Code hook entries
 that feed the dashboard — do not run it when the `ccam` plugin is installed, or
 every event is counted twice.
 
+### Run as a service (auto-start on boot)
+
+`npm start` only runs while that terminal (or `ccam start`'s background
+process) is alive — a reboot loses it. On Linux, `ccam service install` sets
+up a systemd `--user` service instead, so `:4820` is up again on its own after
+every reboot, with no manual step and no Claude Code (or any AI tool) needed
+to trigger it:
+
+```bash
+npm run build              # the service serves the built client, same as npm start
+ccam service install       # writes + enables ~/.config/systemd/user/ccam.service
+ccam service status        # systemctl --user status ccam
+ccam service uninstall     # disable and remove it
+```
+
+`ccam service install` also tries `loginctl enable-linger` so the service
+starts on a cold boot, before anyone logs in; if that needs elevated rights on
+your machine it prints the `sudo loginctl enable-linger <user>` command to run
+once yourself. Plugin installs get the same persistence automatically — see
+[Auto-start on boot](docs/PLUGINS.md#auto-start-on-boot) in `docs/PLUGINS.md`.
+
 ## The CLI
 
 `ccam` is linked by `npm run setup`; otherwise call `node bin/ccam.js`.
@@ -78,6 +99,7 @@ every event is counted twice.
 ```bash
 ccam status            # is the dashboard up
 ccam start             # start it in the background and wait for healthy
+ccam service install   # auto-start on boot via systemd --user (Linux)
 ccam sessions          # recent sessions
 ccam lanes             # lanes with stage and progress
 ccam lanes pipeline    # this lane's pipeline template, or switch it