fix(tui): restore terminal on Ctrl-C when bubbletea shutdown stalls

[dgageot]

Problem

When the user hits Ctrl-C in the TUI and confirms the exit, the terminal is sometimes left in a broken state — raw mode still on, alt-screen still active, mouse tracking on, cursor hidden, etc.

Root cause

The shutdown safety net in appModel.cleanupAll was implemented as:

go func() {
    time.Sleep(shutdownTimeout)
    exitFunc(0)
}()

It exists because bubbletea's renderer can deadlock during shutdown when stdout is wedged (the final flush after tea.Quit re-acquires the renderer mutex still held by a blocked previous flush — TestExitDeadlock_BlockedStdout proves it). But:

• It always sleeps the full timeout, even on a clean shutdown — leaks a goroutine until the process exits.
• os.Exit(0) runs no defers, so the terminal stays in raw mode + alt-screen + mouse tracking + hidden cursor + kitty keyboard flags + …

Fix

Race program.Wait() against the deadline so a clean shutdown skips the force-exit path entirely:

select {
case <-done: // Wait() returned, bubbletea cleaned up normally
case <-time.After(timeout):
    go func() { _ = program.ReleaseTerminal() }()
    exit(0)
}

Program.ReleaseTerminal() is bubbletea's own terminal-restore primitive (out of raw mode, alt-screen exit, cursor on, mouse off, etc.) and is independent from the regular shutdown path. It can itself deadlock on the wedged renderer mutex, so it's run in a fire-and-forget goroutine — best-effort terminal restore, then exit no matter what.

Side fix: shutdownTimeout and exitFunc are package globals that tests mutate; they're now snapshotted synchronously inside cleanupAll so the safety-net goroutine can't race with t.Cleanup restoring the originals.

Tests

New tests in pkg/tui/tui_exit_test.go, all passing under -race:

• TestCleanupAll_SpawnsSafetyNet — stuck program → exitFunc fires.
• TestCleanupAll_GracefulShutdownSkipsExit — clean shutdown → exitFunc does NOT fire.
• TestCleanupAll_NilProgramIsSafe — no program → no safety-net spawned.
• TestCleanupAll_WedgedStdoutFiresExit — realistic regression test: bubbletea is stuck on a wedged stdout, Wait() never returns, ReleaseTerminal() would itself deadlock — exitFunc must still fire. Verified to fail under the previous inline ReleaseTerminal call.

Validation

• task lint ✅
• task test ✅
• go test ./pkg/tui -race ✅