fix(tui): handle form clipboard shortcut - #43526

What

Ctrl+V now pastes clipboard text into the standard V2 TUI form. When a configured choice is focused, the paste automatically opens Type your own answer, inserts the text, and selects that custom answer without submitting.

Before / After

Before: Bracketed terminal paste worked, but the configured prompt.paste shortcut was only owned by the normal prompt. While FORM_MODE was active, pressing Ctrl+V did nothing and Type your own answer remained unchanged.

After: The form registers prompt.paste in FORM_MODE, reads the TUI clipboard service, and routes plain text into the active form editor. Choice fields open the custom-answer row; an already-open textarea receives the text at its cursor.

How

• packages/tui/src/routes/session/form.tsx shares custom-answer insertion between bracketed paste and clipboard-command paste.
• Clipboard text receives the same ANSI stripping and newline normalization as terminal paste bytes.
• The form's prompt.paste command is active only while an answer field is displayed.
• packages/tui/test/cli/tui/form.test.tsx supplies real clipboard content and exercises Ctrl+V through the configured keymap.

Scope

• This PR changes the standard V2 TUI form only.
• Browser app and Mini TUI behavior are unchanged.
• Non-text clipboard content remains ignored.

Testing

• bun run test test/cli/tui/form.test.tsx in packages/tui (20 passed)
• bun typecheck in packages/tui
• Push hook full-repo typecheck (33 tasks passed)
• Live bun run dev:live PTY verification using OS clipboard content and an actual Ctrl+V keypress

Demo

Standard V2 TUI after ctrlv-target was placed on the OS clipboard and pasted with Ctrl+V while the first configured choice was focused:

Flow

sequenceDiagram
  participant User
  participant Keymap
  participant Form
  participant Clipboard

  User->>Keymap: Ctrl+V
  Keymap->>Form: prompt.paste in FORM_MODE
  Form->>Clipboard: read()
  Clipboard-->>Form: text/plain
  Form->>Form: normalize and open custom answer