feat(tui): bare /details opens a keyboard selector

DetailsDialog is a centered SelectList over the five transcript-detail
states (three tool-card phases, reasoning shown/hidden); it preselects
the current phase, marks both current values, applies on Enter, and
cancels on Esc/Ctrl+C. Width is the new detailsDialogWidth config key.
The argument grammar is unchanged and shares the same setters.

packages/ui/tui/tests/tui.snapshot.ts

@@ -46,6 +46,7 @@ const CHECKPOINTS = [
   'advanced-cards-expanded',
   'tool-cards-hidden-folded',
   'details-command',
+  'details-selector',
   'untrusted-controls',
   'question-dialog',
   'question-dialog-single-option',
@@ -661,11 +662,14 @@ describe('TUI terminal-state snapshots', () => {
       harness.terminal.send('/details hidden reasoning off')
       harness.terminal.send('\r')
     })
+    await checkpoint('details-command', harness.terminal, { includeScrollback: true })
+    // Bare /details opens the selector, preselecting and marking the current
+    // hidden/reasoning-off state.
     await renderAfter(harness, () => {
       harness.terminal.send('/details')
       harness.terminal.send('\r')
     })
-    await checkpoint('details-command', harness.terminal, { includeScrollback: true })
+    await checkpoint('details-selector', harness.terminal, { includeScrollback: true })
     nowSpy.mockRestore()
     await disposeSnapshot(harness)
   })