fix(web): polish AskUserQuestion selection

[LIUXIN557]

Summary

• remove visible row borders from hover, selected, and keyboard-focused question options
• allow multi-select custom answers to be unchecked while retaining a muted draft
• keep re-focusing the custom input as the explicit reactivation path
• add horizontal spacing between the in-session question picker and adjacent panels
• extend layout and interaction regression coverage

Verification

• node src/lib/questionPicker.test.js
• node src/lib/questionPickerLayout.test.js
• node src/lib/questionPickerInteraction.test.js
• node src/lib/composerEditabilityArchitecture.test.js
• pnpm build

Temporary mdast patch/lockfile validation changes are not included in commit 5624579a.