feat: add curriculum vitae page with secure download

Add dedicated CV page for HR professionals and recruiters with secure Tresorit download link.

Changes:
- Add CV content page at /cv/ with German text
- Configure CV navigation menu item "Curriculum Vitae"
- Enhance navigation template with active state handling for menu items
- Add secure external link with target="_blank" and security attributes (noopener, noreferrer, nofollow)
- Include email verification notice and information about certificates/references availability
- Create OpenSpec proposal for content-management capability

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Co-Authored-By: Claude <noreply@anthropic.com>

openspec/changes/add-cv-page/proposal.md

@@ -0,0 +1,18 @@
+# Add CV Page
+
+## Why
+The site currently lacks a dedicated curriculum vitae page for HR professionals and recruiters. A CV page with secure download instructions and a navigation menu entry will make the site more complete and professional, enabling visitors to easily access professional credentials.
+
+## What Changes
+- Add new CV content page at `/content/cv.md` with German text explaining secure CV download process
+- Add CV navigation link to site menu configuration in `hugo.toml`
+- Content will explain Tresorit secure download process and email verification requirement
+- Page will follow existing single.html layout pattern with centered, readable content
+
+## Impact
+- Affected specs: `content-management` (new capability)
+- Affected code:
+  - `/content/cv.md` (new file)
+  - `/hugo.toml` (menu configuration)
+  - `/layouts/partials/nav.html` (already supports menu items via iteration)
+- User-facing: New "Lebenslauf" navigation link and dedicated CV page