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.config.ts

@@ -61,7 +61,7 @@ export default defineContentConfig({
     }),
     experiences: defineCollection({
       type: 'data',
-      source: 'experiences/*.json',
+      source: 'experiences/*.md',
       schema: z.object({
         title: z.object({
           en: z.string(),