feat(markdown): support kbd tag rendering

[heartacker]

Pull Request

Description

Add support for rendering <kbd> tags in both chat messages and document preview markdown views.

• Update default rehype plugins pipeline to include rehype-raw with rehype-sanitize allowing <kbd> while keeping malicious scripts/attributes stripped.
• Add keyboard key styling for .markdown-shadow-body kbd and .aionui-markdown :where(kbd) with subtle borders, background, monospace typography, and light/dark theme adaptability.
• Add test coverage verifying <kbd> tags are properly preserved in preview and default markdown pipelines.

Related Issues

• None

Type of Change

• feat — New feature (non-breaking change which adds functionality)

Atomic PR Checklist (Rule 1)

• This PR contains exactly one feature or bug fix that cannot be further decomposed
• The PR title follows Conventional Commit format: <type>(<scope>): <subject> (English)

Local Checks (Rule 3)

• bun run format — formatting passes
• bun run lint — no lint errors (skip if no .ts/.tsx changed)
• bunx tsc --noEmit — no type errors (skip if no .ts/.tsx changed)
• bunx vitest run — tests pass
• i18n validated (bun run i18n:types + node scripts/check-i18n.js) — N/A (no user-facing text strings added)
• New/changed user-facing text uses i18n keys (no hardcoded strings)

Runtime Verification

• Verified on Linux
• I have performed a self-review of my own code

[heartacker]

@tcp404 PTAL, thanks!

[codecov]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...enderer/components/Markdown/markdownComponents.tsx	50.00%	0 Missing and 2 partials ⚠️

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