fix: prevent exit input events from being swallowed - #90

The input handling in run_loop could consume keyboard events without processing them.

process_input() would read one event, and then run_loop() would drain the remaining pending events. Keyboard events encountered by this second loop were discarded, which could cause q, Esc, or Ctrl+C to be ignored. This made quitting tarts unreliable and sometimes required multiple key presses.

This change moves all event handling into process_input(), including:

q, Esc, and Ctrl+C quit handling
Terminal resize handling
Processing all pending events in a single place

This prevents keyboard events from being silently swallowed and makes quitting reliable.