fix: Fix reflected XSS in blog search and emit search

[RaminNietzsche]

Summary

Fixes reflected XSS in blog search and replaces hand-built JSON templates
that could break the search index when post titles contain quotes or special
characters.

Problems

1. Reflected XSS via ?q= parameter

The raw search query from urlParams.get('q') was interpolated into HTML
and assigned via innerHTML without escaping. A crafted URL could execute
arbitrary JavaScript in the visitor's browser.

2. Fragile search JSON generation

search-raw.html and search-output.html built JSON by string concatenation.
Post titles or content with " or control characters produced invalid JSON,
causing scripts/search-index.js to fail at build time.

3. Broken fetch mode (same as #1091)

mode: 'no-cors' on same-origin fetch calls returned opaque responses,
making .json() fail on every search query.

Changes

• src/js/search-output.js: add escapeHtml(), use safeQuery in output;
  remove no-cors / credentials: 'include' from fetch
• Replace search-raw.html / search-output.html with .11ty.js templates
  that emit JSON via JSON.stringify()
• Use locale-aware collection tag ({locale}-blog-post)

Overlap with upstream

This overlaps with open PR #1091 (XSS + fetch fix in search-output.js).
This PR adds safe JSON generation, which #1091 does not cover.

[ceph-jenkins]

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[RaminNietzsche]

@ceph/ceph-website