fix(editor): add code block highlighting and controls

[khoinguyenpham04]

What does this PR do?

Fixes code blocks in the admin and inline visual editors so supported languages are syntax-highlighted on borderless light and dark surfaces. It also adds matching controls for choosing a language and copying code while preserving unsupported language values as plain text.

This is the bottom pull request in the code-block editor stack. The focused visual-polish follow-up is #2603.

Closes #2361

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 — verified for the affected admin and core packages
• 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). No catalog files are included.
• I have added and reviewed the user-facing changeset (if this PR changes a published package) — .changeset/bright-code-blocks.md and .changeset/gentle-code-block-controls.md
• New features link to an approved Discussion: N/A — this fixes existing editor behavior

AI-generated code disclosure

• This PR includes AI-generated code — model/tool: OpenAI GPT-5.6 Codex, reviewed with GPT-5.6 Terra xhigh

Screenshots / test output

• Type-aware lint passed.
• Admin and core typechecks passed.
• Admin editor tests: 71 passed.
• Inline code-block tests: 9 passed.
• Admin and core builds completed.
• Browser-verified syntax highlighting, themes, copy feedback, language selection, responsive placement, and RTL behavior in both editors.
• The focused Playwright suite is included; its isolated local runner is currently blocked by the existing fixture-dependency build step, so the equivalent flows were also verified directly against the local app.

[changeset-bot]

🦋 Changeset detected

Latest commit: 2f2aab6

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

This PR includes changesets to release 17 packages

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

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

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[github-actions]

Scope check

This PR changes 2,657 lines across 19 files. Large PRs are harder to review and more likely to be closed without review.

If this scope is intentional, no action needed. A maintainer will review it. If not, please consider splitting this into smaller PRs.

See CONTRIBUTING.md for contribution guidelines.

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commit: 2f2aab6