Add the Security section to the documentation - #88

Adds Documentation → Security with three pages, per .agents/tasks/security-docs-tasks.md (part 1):

What changed

• remote-markdown shortcode (docs/layouts/_shortcodes/): fetches a Markdown file with resources.GetRemote and renders it into the page, headings and TOC included. The org-wide SECURITY.md stays the only source of the policy text; there is no copy to drift.
  • A failed fetch (network error or HTTP 404) fails the build, so the page never ships empty. Under hugo server it's a warning plus a link to the file, so offline authoring still works.
  • It's a shortcode in a real policy.md, not a content adapter: adapter pages have no .File, and the site-commons sidenav finds the current section from .File.Path.
• Verifying artifacts page: what is attested, what a passing check does and doesn't prove, prerequisites, the command with a worked example, why each flag is there, choosing the branch, an "If the check fails" section, and optional --signer-digest pinning. Adapted for consumers from the config README; maintainer-only details are left out.
• CVD Policy page: the body is byte-identical to spine.io's; only the front matter changed (docs headline, a description, same lastmod, has_numbered_headings kept).
• Navigation: Security comes last, after the Validation guides. The theme always lists the main sidenav before module sidenavs, so Security has its own docs/data/docs/security/sidenav.yml, placed by moduleOrder in docs/hugo.toml.
• Preview config: [caches.getresource] maxAge = '1h'. Hugo's default never expires fetched files, and the check-links workflow restores the Hugo cache between runs, so it would otherwise keep serving the first SECURITY.md forever.
• date shortcode for the preview: the moved page uses it. spine.io has its own with the same output, which takes precedence there.

Other commits on this branch

• Update config and Select CodeMatters (c) profile: the config submodule update and the IntelliJ copyright profile switch.
• Update copyright headers: a repo-wide refresh to the CodeMatters notice (build scripts, samples, one JS file).
• Add task doc for the Security section: the task document, updated in the last commit with the decisions and the merge order.

Merge order: spine.io follow-up

The redirect lives in spine.io, which serves /cvd-policy/ today. Its branch security-section (not pushed yet) does the following:

• deletes the old page and adds a static redirect /cvd-policy/ → /docs/security/cvd-policy/;
• updates the footer link and the Policy: line of security.txt (also fixes its invalid Expires: timestamp);
• makes the docs layout honour has_numbered_headings and fixes the numbered-TOC CSS;
• adds the same cache expiry;
• adds a workflow_dispatch deploy trigger, limited to master, to publish SECURITY.md changes.

Merge this PR first. The spine.io PR must then add a bump of the documentation module pin. Without it, /cvd-policy/ would redirect to a page that doesn't exist yet.

Parts 2 (.github SECURITY.md pointer) and 3 (config README) wait until the pages are live.

Verification

• hugo (production) build of the preview: no errors or warnings, 95 pages.
• spine.io built against this branch via HUGO_MODULE_REPLACEMENTS: pages, sidenav order and expansion, prev/next chain, redirect (with and without the trailing slash), footer, and numbered headings and TOC all checked in a browser.
• Shortcode failure paths tested in a scratch site: HTTP 404 and an unreachable host fail the build; hugo server warns and shows the fallback.
• Link check (lychee, CI configuration): 0 broken links.
• A review-docs pass; its findings were applied.

Note for reviewers

The Security policy page renders SECURITY.md from master of SpineEventEngine/.github, and the site renders raw HTML in Markdown. That branch needs a ruleset, which is listed in the task document's preconditions.

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