Add a system to automatically render Specification Enhancement Proposals
(SEPs) as nicely formatted documentation pages on the website, similar to
how Python renders PEPs.

Changes:
- Add scripts/render-seps.ts to parse SEPs and generate MDX documentation
- Add GitHub workflow to auto-render SEPs when seps/ directory changes
- Generate SEP index page with tabular overview at /community/seps/
- Generate individual SEP pages with metadata badges and formatted content
- Add badge snippet component for status/type badges
- Update docs.json navigation to include SEPs section under Community tab
- Add npm scripts: generate:seps and check:seps

Address GitHub Advanced Security comment by adding explicit permissions
block to the workflow. The workflow requires 'contents: write' to push
auto-rendered SEP documentation on the main branch.

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The render-seps script now automatically formats generated MDX files
with Prettier to ensure they pass the format check. In check mode,
it compares files after applying Prettier formatting to handle any
formatting differences.

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Use semi-transparent backgrounds (500/20) and brighter text (400) in
dark mode for better contrast and readability instead of the previous
dark backgrounds (900) with light text (200).

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Mintlify doesn't support all Tailwind dark: classes, so switch to
inline CSS with explicit hex colors. Targets multiple dark mode
selectors (.dark, [data-theme="dark"], prefers-color-scheme) for
compatibility.

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Co-Authored-By: Claude <noreply@anthropic.com>