chore: drop stale .gitignore entry for the removed Kotlin TUI

apps/tui (the pre-Go-rewrite Kotlin TUI) is already gone — not on disk, not
tracked, and not in settings.gradle — so its runtime-logs ignore rule pointed
at a path that no longer exists. The apps/tui mentions in docs/epics/epic-13*
are left as historical record.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -76,9 +76,6 @@ current.log
 # Go TUI build output
 apps/tui-go/bin/
 
-# TUI runtime logs (Kotlin TUI, pre-Go rewrite)
-apps/tui/logs/
-
 # Server runtime logs
 apps/server/logs/