Add canonical link injection to public CV pages

[vincentmakes]

Description

Adds <link rel="canonical"> tag injection to public CV pages to prevent search engine indexing of duplicate content across URL variants. The canonical link is derived from the request and respects reverse-proxy headers (X-Forwarded-Proto and X-Forwarded-Host), consistent with how /sitemap.xml and /robots.txt are already handled.

Behavior:

• Public root (/) and live-CV fallback pages always emit a canonical link
• /v/:slug pages emit a canonical link only when slugsIndex setting is enabled
• When slugsIndex is disabled, /v/:slug pages receive noindex, nofollow robots meta tag instead

Implementation:

• New buildCanonicalTag(req) helper function in src/server.js that constructs the canonical URL from request headers and path
• Canonical injection applied at all three SSR injection points in servePublicIndex() and serveDatasetPage()
• Query strings and fragments are stripped (uses req.path)

Type of Change

• New feature (non-breaking change that adds functionality)

Checklist

Required for all code changes

• I have tested my changes locally (npm test passes)
• Version has been bumped in all 3 files (package.json, package-lock.json, version.json)
• CHANGELOG.md has been updated with a new entry under the correct version

If adding or changing user-visible strings

• No user-visible strings added (canonical links are SEO metadata, not UI text)

Test Coverage

Added comprehensive test suite covering:

• Canonical link emission on public root with X-Forwarded-Host
• Protocol and host header handling (X-Forwarded-Proto and X-Forwarded-Host)
• Canonical omission on /v/:slug when slugsIndex is disabled (with noindex verification)
• Canonical emission on /v/:slug when slugsIndex is enabled

All tests pass with npm test.

https://claude.ai/code/session_01EGykcv9Yvem218n13TqYhz