feat(tui): standardize dialog footer actions behind new designs experiment - #55806

Stack (merge bottom-up):

• feat(tui): new dialog designs behind new designs experiment #55810 Agent colors
• feat(tui): restyle dialog headers behind new designs experiment #55809 Header styling
• feat(tui): show list overflow indicator behind new designs experiment #55808 List overflow indicator
• feat(tui): style selected dialog list rows behind new designs experiment #55807 Selected list rows
• feat(tui): standardize dialog footer actions behind new designs experiment #55806 Footer actions 👈 this PR
• feat(tui): raise dialog footers behind new designs experiment #55805 Footer band
• refactor(tui): read the new designs experiment through useNewDesigns #55802 useNewDesigns()
• feat(tui): hide dialog search on short lists behind new designs experiment #55801 Hide search on short lists
• feat(tui): put dialog search in the title row behind new designs experiment #55800 Search in the title row
• refactor(tui): build DialogSelect on DialogLayout #55799 DialogSelect on DialogLayout
• feat(tui): add opencode2 theme and text.faint token #55798 opencode2 theme + text.faint
• feat(tui): add new designs experiment #55818 New designs experiment
• dev

Issue for this PR

N/A. Part of the new dialog designs.

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Footers take data instead of JSX:

<DialogLayout footer={{ actions: { secondary: [...], primary: [...] } }} legacyFooter={<old JSX>} />

Secondary actions sit on the left (dialog-level), primary on the right (selected item / main action). legacyFooter keeps the old UI with the experiment off and goes away when it graduates.

Under the experiment:

• Custom button footers (alert, confirm, help, export, update, delete worktree, highlights) become standard label key actions.
• Actions have a hover state and faint shortcut labels.
• Navigation-only hints (scroll, esc back, change ←/→) are removed.
• Labels and keys follow the designs (connect integration, remove account, open link enter, delete d, copy c).

New key bindings only apply under the experiment; production keybinds are unchanged.

DialogPrompt's extra actions (e.g. worktree name's generate) go into the primary group to the left of submit, matching the design (generate name tab submit enter). The legacy footer keeps the current order.

Note: the hover is only visible in opencode2 for now. Other themes map dialog action hover to the band color; fixing that touches production themes, so it's left for later.

How did you verify your code works?

Rendered the affected dialogs before and after with the experiment off and compared the frames (text and colors); they are identical. Typecheck and TUI tests pass apart from the two shell-output tests that also fail on dev. Tested the experiment-only bindings (delete worktree d, esc, enter) on and off, and hover with a mock mouse in opencode2.

Screenshots / recordings

None yet. All visual changes are behind the new-designs experiment (Experiments dialog → New designs, then pick the opencode2 theme).

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR