[sank8-2]

Description

Closes #289

Adds the blog-updated-post template for refreshed posts that want to say what changed: an "Updated" label in the accent, the post title large under it, a dates line ("First published …" · "Updated …"), up to three short "What changed" lines, and the site name at the bottom.

• Blank change lines are skipped with no gaps; the "What changed" heading hides when all three are blank.
• Empty or whitespace-only published, updated, or site name hide cleanly (no stray separator).
• Long titles shrink with autoFontSize() and then truncate; change lines and the site name truncate too.
• The label and accent text stay readable on light and dark backgrounds via contrastText / mixColors.

How I Tested This

• npm run check — 0 errors (pre-existing hints only).
• npm test -- tests/templates/updated-post.test.ts — 15 tests passed (registration/re-export, 1200×630 root, flex on every div, defaults order, blank change skipping, heading hide, empty dates/site name, long title shrink+truncate, light/dark contrast).
• npm run check re-run after registering in blog/index.ts and registry.ts.

AI Assistance

OpenCode drafted the template and tests; Cursor helped move the work onto a dev-based branch and resolve export/registry conflicts. I reviewed the diff and ran the checks above locally.

Type of Change

• New template

Checklist

• This PR targets dev
• I was assigned the linked issue
• npm run check passes
• npm run test passes with the default timeout
• Tested locally
• New template follows the Template Guidelines