feat(tui): replace /clear double-press gate with a proper confirm overlay

The time-window gate felt wrong — users would hit /clear, read the
prompt, retype, and consistently blow past the window. Swapping to a
real yes/no overlay that blocks input like the existing Approval and
Clarify prompts.

- add ConfirmReq type + OverlayState.confirm + $isBlocked coverage
- ConfirmPrompt component (prompts.tsx): cancel row on top as the
  default, danger-coloured confirm row on the bottom, Y/N hotkeys,
  Enter on default = cancel, Esc/Ctrl+C cancel
- wire into PromptZone (appOverlays.tsx)
- /clear + /new now push onto the overlay instead of arming a timer
- HERMES_TUI_NO_CONFIRM=1 still skips the prompt for scripting
- drop the destructiveGate + createSlashHandler reset wiring
  (destructive.ts and its tests removed)

Refs #4069.

ui-tui/src/components/appOverlays.tsx

@@ -9,7 +9,7 @@ import { $uiState } from '../app/uiStore.js'
 import { FloatBox } from './appChrome.js'
 import { MaskedPrompt } from './maskedPrompt.js'
 import { ModelPicker } from './modelPicker.js'
-import { ApprovalPrompt, ClarifyPrompt } from './prompts.js'
+import { ApprovalPrompt, ClarifyPrompt, ConfirmPrompt } from './prompts.js'
 import { SessionPicker } from './sessionPicker.js'
 import { SkillsHub } from './skillsHub.js'
 
@@ -31,6 +31,23 @@ export function PromptZone({
     )
   }
 
+  if (overlay.confirm) {
+    const req = overlay.confirm
+
+    const onConfirm = () => {
+      patchOverlayState({ confirm: null })
+      req.onConfirm()
+    }
+
+    const onCancel = () => patchOverlayState({ confirm: null })
+
+    return (
+      <Box flexDirection="column" flexShrink={0} paddingX={1} paddingY={1}>
+        <ConfirmPrompt onCancel={onCancel} onConfirm={onConfirm} req={req} t={ui.theme} />
+      </Box>
+    )
+  }
+
   if (overlay.clarify) {
     return (
       <Box flexDirection="column" flexShrink={0} paddingX={1} paddingY={1}>