test: add E2E tests for callout and collapsible blocks (#222)

[zacharias-ona]

Closes #222

What

Adds E2E test coverage for callout and collapsible/toggle editor blocks — two interactive features where bugs would only manifest in a real browser (previous issues #204, #206 were caught by users, not tests).

Tests added

1. Callout block — inserts via /callout slash command, verifies it renders with distinct styling (border-l-2, bg-muted, emoji span) and is not a code block element.
2. Toggle expand/collapse — inserts via /toggle slash command, verifies the <details> element starts open, collapses when the chevron is clicked, and re-expands on a second click.
3. Toggle content persistence — types custom text inside the collapsible content area, then collapses and re-expands to verify the content persists across toggle cycles.

Testing

• pnpm lint ✅
• pnpm typecheck ✅
• pnpm test — 252 unit tests pass ✅
• pnpm test:e2e — 60 E2E tests pass (57 existing + 3 new) ✅

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Project	Deployment	Actions	Updated (UTC)
memo	Ready	Preview, Comment	Apr 18, 2026 7:39am

[zacharias-ona]

Reviewed — all three acceptance criteria from #222 are covered. The insertViaSlashCommand helper follows the established pattern from editor-slash-commands.spec.ts. Assertions check DOM structure, attributes, visibility, and text content. No issues found. Merging.

[zacharias-ona]

✅ Post-merge verification skipped — test: PR does not affect the live app.

[zacharias-ona]

✅ UI verification skipped — no UI files changed (only E2E test files).