feat(tui): event-derived ordering + retire Kotlin TUI

Rebuild the Go TUI transcript from the event stream instead of
optimistic local echoes. ChatTurnEvent now maps to ServerMessage.ChatTurn
(chat.turn); the TUI auto-vivifies sessions and renders user+router turns
from events. SessionStarted is de-special-cased into SessionAnnounced
(still carries workflowId), dropping the router.response shadow and
optimistic echoes.

Delete the unused Kotlin TUI (apps/tui) and add a kotlinx<->Go
golden-fixture test to lock the wire protocol. Gitignore server runtime
logs.

.gitignore

@@ -78,3 +78,6 @@ apps/tui-go/bin/
 
 # TUI runtime logs (Kotlin TUI, pre-Go rewrite)
 apps/tui/logs/
+
+# Server runtime logs
+apps/server/logs/