feat(fleet): add durable tmux fleet poc

scratchpads/2026-06-19-tmux-fleet-durable-install-plan.md

@@ -715,7 +715,7 @@ The implementation is complete when:
 ## Risks and mitigations
 
 | Risk                                                | Mitigation                                                                        |
-|---|---|
+| --------------------------------------------------- | --------------------------------------------------------------------------------- |
 | Killing existing tmux sessions                      | Use named `mosaic-factory` socket; no default `tmux kill-server`.                 |
 | systemd unit quoting/env expansion bugs             | Move logic into shell wrappers; verify with `systemd-analyze --user verify`.      |
 | Runtime reset command mismatch                      | Make reset command runtime-configurable; fallback to service restart + kickstart. |