fix: render extension dialogs inline with keyboard nav, stacking, and expiry (#462)

[mufflegyro]

Closes #462

Summary

ctx.ui.select() / confirm() / input() / editor() dialogs were rendered as a full-window overlay that hid the chat context, ignored the timeout/expiresAt fields in the protocol, offered no keyboard support for select, and used a single state slot that couldn't express composed flows. This PR implements all three proposed steps (P0 + P1 + P2) from the issue.

Changes

P1 — Inline cards in the transcript

• Dialogs now render as inline cards in the conversation transcript (message stream, plus the new-session state below the composer) instead of a dimming position:absolute; inset:0 overlay. The conversation stays readable while answering; no overlay, no click-outside needed.
• Dropped aria-modal="true": the card is intentionally non-modal (role="dialog" + aria-label instead).

P0 — Keyboard navigation + Esc

• select supports Arrow Up/Down (and Left/Right), Home/End, Enter to pick the highlighted option, and Esc to cancel. Hover syncs the active option.
• The global stop-agent Esc shortcut now yields when focus is inside an extension dialog (hooks/useKeyboardShortcuts.ts), so Esc cancels the dialog instead of aborting the run.

P2 — Dialog stack + timeout/expiresAt

• Unanswered dialogs queue in a stack instead of clobbering each other, so composed flows (select → input) and pipelined requests from concurrent extensions resolve in order. Entries are deduped by request id because the events stream replays pending requests on reconnect (hooks/useAgentSession.ts).
• Dialogs carrying timeout/expiresAt show a live countdown ("expires in Ns") and auto-cancel at the deadline, resolving the extension's await with its default value — matching the daemon-side timeout and the TUI's auto-dismiss. Stale dialogs are dropped when switching sessions.

Verification

• tsc --noEmit, eslint ., and the full test suite (844 tests) pass.
• End-to-end with a real extension command on the running dev instance (playwright, headless chromium):
  • Keyboard select → input composed flow round-trips the user's actual answers back to the extension;
  • Esc cancels the select (notify received);
  • a 6s timeout shows the countdown, auto-dismisses, and notifies the extension;
  • two queued dialogs show one active card + a "N more pending" indicator and resolve sequentially;
  • a page reload (SSE reconnect) replays only one dialog card (dedupe).

Notes

• ExtensionCustomPanel (custom UI method) is intentionally left as an overlay — out of scope for this issue.
• The select options list caps at maxHeight: 260 with internal scroll (replaces the old flex: 1 overlay cap); the card is maxWidth: 560, width: 100%.

[agegr]

Closing this PR in favor of the existing #612 changes and 2356904 on main.

#612 already provides collapsible dialogs that keep the composer and Stop accessible, plus server-driven dialog closure on timeout/cancellation. The new commit adds arrow-key and Home/End navigation with visible native button focus, scrolls the focused option into view, handles Escape inside the dialog without aborting the agent, and displays a localized countdown from the server's expiresAt value. Expiry remains owned by the server through extension_ui_closed.

The inline layout and preemptive dialog stack are not being adopted here. Review reproduced cancellation leaking from an expired request into an unrelated queued request, loss of a queued dialog's draft, and keyboard selection moving offscreen. Concurrent request queuing can be addressed separately; sequential select-to-input flows already work without a stack.

Validation: TypeScript, ESLint, and all 891 tests pass. The browser suite passes at 1280px and 390px, including real extension commands for navigation, Escape without agent abort, draft preservation across collapse/expand, countdown updates, and answering a new request after server-side expiry. These checks are now retained in the E2E suite.