Fixes three critical bugs that caused crashes after long-running:
1. Use-after-free race condition in room_broadcast()
- Added reference counting to client_t structure
- Increment ref_count before using client outside lock
- Decrement and free only when ref_count reaches 0
- Prevents accessing freed client memory during broadcast
2. strtok() data corruption in tui_render_command_output()
- strtok() modifies original string by replacing delimiters
- Now use a local copy before calling strtok()
- Prevents corruption of client->command_output
3. Improved handle_key() consistency
- Return bool to indicate if key was consumed
- Fixes issue where mode-switch keys were processed twice
Thread safety changes:
- Added client->ref_count and client->ref_lock
- Added client_release() for safe cleanup
- room_broadcast() now properly increments/decrements refs
This fixes the primary cause of crashes during extended operation.
