fix(annotate): make Ask AI announcement provider cards clickable (#972)

[backnotprop]

Fixes #972

Problem

The PlanAIAnnouncementDialog (the one-time "New: Ask AI for annotated documents" popup) shows provider cards — Claude, OpenCode, Pi, Codex — with clear selection styling: one card reads "SELECTED" while the others look unselected. This strongly implies the cards are clickable to switch the active AI provider.

They weren't. Each card was a plain <div> with no onClick, so clicking did nothing. A user with both Claude Code and OpenCode installed (Plannotator auto-detects claude-code as origin) would see OpenCode sitting right there, click it to switch, and get no response — the affordance lied.

Fix

• Provider cards now render as <button>s for actually-detected providers and call the existing AI config change handler — the same path used by the Settings provider selector (handleAIConfigChange → saveAIProviderSelection).
• Selection state was already lifted in App.tsx, so the "SELECTED" badge updates live on click — no new state needed.
• Providers that aren't installed are shown greyed out with a "not installed" label instead of looking selectable, since the dialog's card list is the full set of supported provider types, not just the detected ones.
• The dialog is fed the raw detected provider list (aiProviders) rather than visibleAIProviders, so the agent-terminal substitution doesn't collapse the list to a single pseudo-provider and make every card read "not installed".

Note on the report's "additional issue" (buttons unresponsive in --render-html)

The report also claimed that in --render-html mode the embedded iframe captured pointer events, making all dialog buttons (including Dismiss) unresponsive.

I could not reproduce this. The dialog renders as a portal overlay above the iframe at z-[100], which receives clicks normally — and manual testing (annotate <file.html> --render-html --gate, fresh incognito session) confirmed Dismiss, Open AI Chat, and the cards all work. The reported symptom was the dead-cards bug above: clicking the cards did nothing, which read as "the whole dialog is frozen." This change resolves it; no iframe/layering change was needed.

Testing

• tsc --noEmit clean for packages/ui
• build:hook and review app build succeed
• Manually verified in annotate --render-html --gate (incognito): cards switch provider, badge updates, uninstalled providers greyed, Dismiss / Open AI Chat responsive