feat: add multilingual support with German and English

Implement complete multilingual support using Hugo's multilingual mode with German (de) as default and English (en) as secondary language.

Changes:
- Configure Hugo multilingual mode with language-specific parameters
- Reorganize content using language suffix pattern (filename.de.md, filename.en.md)
- Translate all content to English (home page and CV page)
- Implement language switcher that maintains page context
- Add language-specific navigation menus
- Update templates to use language-aware URL functions (relLangURL)
- Fix navbar brand and Home links to respect current language
- Add translationKey to content frontmatter for explicit translation linking

URL Structure:
- German: /de/ (home), /de/cv/ (CV page)
- English: /en/ (home), /en/cv/ (CV page)

Key Implementation Details:
- Use filename.{lang}.md pattern instead of {lang}/filename.md subdirectories
- Always use relLangURL for internal navigation, never .Site.BaseURL
- Menu URLs must include language prefix when defaultContentLanguageInSubdir = true
- Added translationKey to frontmatter for proper translation discovery

Documented 5 critical bugs and their solutions in design.md for future reference.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

content/_index.en.md

@@ -0,0 +1,17 @@
+---
+description: "Open, honest developer personality striving for meaningfulness."
+---
+
+<div class="row">
+  <div class="col-md-2">
+    <img src="/images/profile/markusgraf.jpg" alt="Portrait photo of Markus Graf" class="img-fluid" />
+  </div>
+   <div class="col-md-10">
+
+## Hey, I'm Markus
+
+- 🧘‍♂️ Open, honest developer personality striving for meaningfulness.
+- 🔬 Experience in academic work and data analysis.
+- 👨‍💻 Over 20 years of experience in the conception, development, and maintenance of software.
+  </div>
+</div>

content/cv.de.md

@@ -1,6 +1,7 @@
 ---
 title: "Curriculum Vitae"
 description: "Curriculum Vitae von Markus Graf"
+translationKey: "cv"
 ---
 
 ## Download

content/cv.en.md

@@ -0,0 +1,19 @@
+---
+title: "Curriculum Vitae"
+description: "Curriculum Vitae of Markus Graf"
+translationKey: "cv"
+---
+
+## Download
+
+The curriculum vitae can be downloaded via the following secure link:
+
+<a href="https://web.tresorit.com/l/khkGf#UBmRnKs_3dkUTZRwtbbdUQ" target="_blank" rel="noopener noreferrer nofollow">Download CV</a>
+
+**Please note:** On first access, you will be asked to verify your email address. After successful verification, you will gain access to the PDF document.
+
+## Certificates and References
+
+Work certificates and references are not included in the public download for privacy reasons. These can be requested personally upon interest.
+
+For questions, I am available at [info@markusgraf.ch](mailto:info@markusgraf.ch) or by phone at [+41 (0)79 261 16 37](tel:+41792611637).