Add Block Kit item list block

[masonjames]

What does this PR do?

Adds the item_list Block Kit block to @emdash-cms/blocks.

This block renders compact entity lists that are richer than fields but less structured than table, such as queues, accounts, imports, plugins, and recent objects. Items support a title, optional description, metadata, badge, short icon text, avatar preview, and nested ButtonElement actions.

Avatar previews are restricted to safe root-relative paths and http(s) URLs. Unsafe preview URLs are suppressed.

Discussion: #904

Closes #

Type of change

• Bug fix
• Feature (requires maintainer-approved Discussion)
• Refactor (no behavior change)
• Translation
• Documentation
• Performance improvement
• Tests
• Chore (dependencies, CI, tooling)

Checklist

• I have read CONTRIBUTING.md
• pnpm typecheck passes
• pnpm lint passes
• pnpm test passes (or targeted tests for my change)
• pnpm format has been run
• I have added/updated tests for my changes (if applicable)
• User-visible strings in the admin UI are wrapped for translation (if applicable). Do not include messages.po changes except in translation PRs — a workflow extracts catalogs on merge to main.
• I have added a changeset (if this PR changes a published package)
• New features link to an approved Discussion: Proposal: Add five practical Block Kit blocks for richer plugin/admin UIs #904

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: Codex GPT-5.5 via RepoPrompt orchestrate/agents; Codex GPT-5 local coding agent

Screenshots / test output

• pnpm --silent lint:quick passed on this branch.
• pnpm --filter @emdash-cms/blocks test passed on this branch.
• pnpm --filter @emdash-cms/blocks typecheck passed on this branch.
• Integration branch codex/blockkit-all-five-integration passed pnpm typecheck.
• Integration branch codex/blockkit-all-five-integration passed pnpm format:check.
• Integration branch codex/blockkit-all-five-integration passed pnpm --filter @emdash-cms/blocks test with 136 tests.
• Integration branch codex/blockkit-all-five-integration passed pnpm --filter @emdash-cms/blocks-playground build.
• Integration browser verification rendered all five proposed blocks together, confirmed unsafe avatar previews are suppressed, and confirmed nested block_action events.
• GitHub CI is passing, including Typecheck, Lint, Tests, Integration Tests, Browser Tests, Smoke Tests, E2E shards, Format, Version Check, Validate Plugins, and Validate PR.

[changeset-bot]

🦋 Changeset detected

Latest commit: aaeebf9

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@emdash-cms/blocks	Patch
@emdash-cms/admin	Patch
emdash	Patch
@emdash-cms/plugin-embeds	Patch
@emdash-cms/cloudflare	Patch
@emdash-cms/fixture-perf-site	Patch
@emdash-cms/perf-demo-site	Patch
@emdash-cms/cache-demo-site	Patch
@emdash-cms/auth	Patch
@emdash-cms/gutenberg-to-portable-text	Patch
@emdash-cms/x402	Patch
create-emdash	Patch
@emdash-cms/auth-atproto	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

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commit: aaeebf9

[github-actions]

Overlapping PRs

This PR modifies files that are also changed by other open PRs:

• Add Block Kit media grid block #908 (8 shared files)
• Add Block Kit checklist block #907 (8 shared files)
• Add Block Kit timeline block #906 (7 shared files)
• Add Block Kit card grid block #905 (8 shared files)

This may cause merge conflicts or duplicated work. A maintainer will coordinate.