[umpireboulianne-design]

Summary

• Update ToastProvider in apps/web/src/ui/Toast.tsx to record the active trigger element when push() is called (including preserving the original opener across working → success/error async transitions).
• Restore keyboard focus to the recorded opener when a toast is dismissed via its close button, via the Escape key (onKeyDown), or when focus was inside the dismissed toast.
• Add automated tests in apps/web/src/ui/Toast.test.tsx (imported by countdown.test.ts so pnpm web:test executes them in CI) covering close-button dismissal, Escape key dismissal, and async working → completion sequences.
• Document toast focus-restoration behavior in docs/DEMO_SCRIPT.md.

Supply-chain review

• No package scripts or dependencies changed. If changed, explain why below.
• No .vscode/, workflow, or other editor/config file changes. If changed, list them below.
• No lockfile changes. If changed, explain the update below.
• No binary or font asset changes. If changed, list and justify them below.
• I confirm no automatic task (such as preinstall/postinstall) was added.
• I confirm no hidden executable payload (encoded blob, obfuscated command, or unexpected binary) was added.
• Any changed executable or binary was reviewed by a maintainer.

Testing

• node --import tsx --test src/ui/Toast.test.tsx in apps/web (3/3 tests pass)
• node --import tsx --test src/lib/countdown.test.ts in apps/web (9/9 tests pass)
• node scripts/check-links.js (passes)

Closes #545
Fixes #545

[karagozemin]

I reviewed the diff and did not find a malicious payload, but this branch now conflicts with current main after related changes landed. Please rebase on current main, preserve the already-merged security and CI gates, rerun the relevant tests, and update this PR; it is not safe to merge the stale conflict state.