Add custom service log file support with L key

- Add ServiceLogConfig structure for per-host service log paths
- Implement L key handler for custom log file viewing via tmux popup
- Update dashboard config to support service_logs HashMap
- Add tail -f command execution over SSH for real-time log streaming
- Update status line to show L: Custom shortcut
- Document configuration format in CLAUDE.md

Each service can now have custom log file paths configured per host,
accessible via L key with same tmux popup interface as journalctl.

shared/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cm-dashboard-shared"
-version = "0.1.49"
+version = "0.1.50"
 edition = "2021"
 
 [dependencies]