docs(vscode): recommend the community VS Code extension

[svg153]

Tracks svg153/nan-vscode#19. Target repository: helmcode/nan.

What

Adds a short, equivalent section to both VS Code guides, right after "What you need" / "Qué necesitas":

• English: src/content/docs/vscode.mdx → "Optional: the community VS Code extension"
• Spanish: src/content/docs-es/vscode.mdx → "Opcional: la extensión comunitaria de VS Code"

Content (both languages):

1. Download the latest .vsix from the svg153/nan-vscode Releases page (no hard-coded version).
2. Extensions: Install from VSIX...
3. NaN Builders: Manage Provider → enter the NaN API key (sk-…), models are fetched from the key.
4. NaN Builders: Refresh Models when access changes.

A <Callout variant="info"> states that svg153/nan-vscode is community-maintained, not an official NaN Builders product, configures chat and agent mode only, does not touch inline completion, and does not replace the manual instructions.

What does not change

• The manual Custom Endpoint instructions stay in place and unchanged as the reference path.
• No Marketplace assumptions (the extension is distributed as a VSIX from GitHub Releases).
• No claims of official support, inline completion, or unshipped capabilities.

Validation

• Links resolve: repository and Releases page (v1.4.0 latest) verified.
• Wording matches the extension README (command names, VSIX flow).
• Local (Windows): npx astro check → 0 errors, npm run build → success. npm test passes 1294/1305; the 11 failures are in src/lib/mdxToText.test.ts and are pre-existing on clean main (CRLF/LF fixture mismatch on Windows, reproduced with this branch stashed).
• Upstream CI (npm test, npx astro check, npm run build on Linux) is the authoritative check for this PR.
• No secrets or user data in the diff.

Acceptance criteria (svg153/nan-vscode#19)

• English guide links to the repository and releases
• Spanish guide contains equivalent instructions and caveats
• No undocumented credential or Marketplace assumption
• Chat/Agent support distinguished from inline completions; labeled community-maintained
• Manual Custom Endpoint instructions unchanged
• Upstream docs checks pass (running on this PR)
• PR links the issue and identifies helmcode/nan as target

[svg153]

Validation follow-up: the 11 failures called out in the description are definitively a Windows EOL artifact, not content failures.

• Clean main (E51666F... wait, e51666f) checked out with LF working tree: npm test → 1305/1305 passed (66 files).
• Root cause: repo-level core.autocrlf was not pinned, so on Windows the src/lib/mdxToText.test.ts fixtures checked out as CRLF while the runtime produces LF. With core.autocrlf=false + re-checkout (LF), all pass.
• npx astro check → 0 errors / 0 warnings (162 files) ✅
• npm run build → Complete ✅

No content changes needed; upstream Linux CI will run against LF regardless.