Refactor experiences data format from JSON to Markdown

- Updated content.config.ts to change experiences source from JSON to Markdown files.
- Deleted JSON files for experiences: artdanjproduction, erisium, picard, and sevetys.
- Created corresponding Markdown files for each experience with structured front matter.
- Added new API endpoints for fetching experiences and projects in Markdown format.
- Removed unused ping API endpoint.
- Updated package.json with new dependencies for AI SDK and Zod.
- Added new resume files in PDF format for M1 2026 in English and French.

content/experiences/erisium.md

@@ -0,0 +1,13 @@
+---
+title: Junior Developer
+description: At Erisium, one of the most popular French-speaking Minecraft servers, I worked as a Junior Java Developer. I developed mini-games designed by the game design team, and worked on backend infrastructure optimizations to handle several thousand concurrent players. This experience allowed me to solve a wide range of complex bugs and to grow within a collaborative, high-performance technical environment.,
+company: Erisium
+companyUrl: https://x.com/Erisium
+location: Remote, France
+startDate: 2021-09
+endDate: 2022-09
+tags: 
+  - java
+  - docker
+  - minecraft
+---