## Summary

Addresses the selected radio dot alignment reported as the second issue
in #62955 (ask_user formatting issues), which is already closed.

Merged PR #63656 fixed long option wrapping by removing label
truncation. That fix was already present in this branch base. This PR
keeps option text rendering unchanged while fixing the remaining radio
alignment issue and extracting the radio behavior into a reusable UI
component.

Original Issue:
<img width="1672" height="844" alt="image"
src="https://github.com/user-attachments/assets/54422dec-f35a-4b83-b16c-831e8755cf50"
/>

After #63656:
<img width="769" height="386" alt="image"
src="https://github.com/user-attachments/assets/f659f518-2b4a-47cc-8e2d-c9d46bbdbe10"
/>


After:
<img width="777" height="385" alt="Screenshot From 2026-09-07 18-05-16"
src="https://github.com/user-attachments/assets/71ee9343-9623-46bc-8be8-09667fab89b6"
/>


## Implementation

- Add a reusable `ui::RadioButton` component that owns the full
option-row hit target, click handling, focus-visible styling,
configurable tab index, accessibility role/state, and theme-derived
radio styling.
- Keep the elicitation form responsible for selection state and the
selection callback while moving the radio control mechanics into
`crates/ui`.
- Paint the outer radio circle and selected dot from the same
pixel-snapped bounds instead of independently laid-out elements.
- Derive the dot using equal whole-device-pixel insets so the outer
circle and selected dot remain concentric when rounded device-pixel
diameters have different parity.
- Preserve the original `size_3()` visual radio inside the 20px control
slot, while the full row remains clickable.
- Provide an explicit accessible label for each radio option and expose
the selected state through `Role::RadioButton` / `aria_selected`.
- Preserve the existing elicitation row spacing, hover styling,
long-option layout, and keyboard navigation behavior.

## Scope

This PR does **not** re-enable the `ask_user` tool or change its default
profile settings. The tool remains opt-in following #63036. Subagent
question visibility and broader radio-group behavior such as
arrow-key/roving-tab-index navigation are outside this change.

## Validation

- `cargo check -p ui -p agent_ui` passed.
- `cargo test -p agent_ui form_choices_are_keyboard_accessible --
--nocapture` passed.
- `rustfmt --edition 2024 --check
crates/ui/src/components/radio_button.rs crates/ui/src/components.rs
crates/agent_ui/src/conversation_view/elicitation.rs` passed.
- `git diff --check` passed.
- Built and ran the updated application locally.
- Manually verified the single-select UI with short and long options:
the selected dot is centered, the visual radio retains its original
size, long option text wraps correctly, and the row layout remains
intact.
- Other display scales have not been visually verified.

Release Notes:

- Fixed selected radio indicator alignment in agent elicitation forms.

---------

Co-authored-by: MrSubidubi <finn@zed.dev>