This change introduces support for YAML-driven startup layouts, allowing users to define complex window and pane configurations that are automatically applied when starting a new session.

Key features:
- CLI support via --layout <name> flag.
- Configuration search order: --layout > local .prise.yml > global layout.yml > built-in.
- Built-in layouts: default, horizontal-split, vertical-split, dev.
- Support for multiple tabs (windows) and sequential pane splits within each tab.
- Variable expansion in commands (/Users/bangedorrunt, nano, /run/current-system/sw/bin/fish, , ).
- Integrated with the tiling UI to automatically spawn PTYS and execute commands.

* Server: Add terminal_mutex locking when accessing PTY title and cwd to prevent data races.
* Client: Use absolute path for exec, ensure proper TTY deinitialization, and fix terminal reinitialization on failure.

The previous implementation allowed concurrent access to PTY state, leading to segfaults. Additionally, the exec call was using a relative path and leaving the TTY in an inconsistent state.

* Server: Added terminal_mutex locking when accessing PTY title and cwd to prevent data races.
* Client: Implemented an RPC send queue to handle concurrent requests safely and prevent hangs during session restoration.
* Client: Improved switchToSession reliability by ensuring TTY thread is stopped and joined before exec, and using absolute path for the executable.
* Client: Added pty_id_map to maintain UI consistency when PTYs are recreated with new IDs after a server restart.
* Lua: Fixed runtime errors in command palette caused by improper string conversion of dynamic command names.

The previous implementation had multiple race conditions in the server and lacked proper flow control in the client RPC layer, leading to segfaults and freezes during heavy I/O or session switching. Lua runtime errors further destabilized the UI during palette operations.