fix(site): normalize release dates and align cast control

[AugustoMarcelo]

Closes #153

Summary:

• Apply existing chip styling to title-detail cast cross-reference buttons.
• Normalize exact date-only and valid ISO release dates to local calendar midnight.
• Keep the next-release card hidden for missing or malformed dates.

Verification:

• yarn lint (pass; 11 pre-existing warnings)
• yarn test (pass; 63 suites, 258 tests)
• yarn build (pass)
• yarn check:surfaces (pass)
• yarn typecheck (blocked by pre-existing errors in unchanged mcuapi-mcp-public/src/index.ts)
• Browser fixture verification in America/Fortaleza: ISO/date-only dates, invalid dates, chip styling, theme toggle, keyboard/click navigation.
• Codex review: no findings.

No API, OpenAPI, client, MCP, snapshot, or surface-manifest changes.

[AugustoMarcelo]

Browser verification evidence (local fixture pages, America/Fortaleza):

• Next-release card with ISO timestamp and local calendar date:

• Cast cross-reference chip styling:

• Interactive focus/click navigation recording:

mcuapi-cross-reference.mp4