Add Makefile, package.json, and initial configuration for VitePress and Slidev integration

- Introduced a Makefile for streamlined commands related to building, running, and managing presentations.
- Created package.json to define project metadata, dependencies, and scripts for development and testing.
- Added .gitignore entries to exclude build artifacts and temporary files from version control.
- Included playwright.config.mjs for end-to-end testing setup with Playwright.
- Added README.md for project documentation, outlining setup instructions and development guidelines.

tools/site-base.mjs

@@ -0,0 +1,30 @@
+/**
+ * Préfixe URL du site, aligné sur VitePress `base`.
+ * Racine : SITE_BASE=/ ou absent
+ * Sous-chemin (ex. GitHub Pages) : SITE_BASE=/mon-repo/
+ *
+ * En dev local (`TALKS_PORTAL_DEV=1`, ex. make run), SITE_BASE est ignoré pour
+ * éviter les modules .md servis en text/html (mismatch base / URLs).
+ * Pour tester un sous-chemin en dev : SKIP_PORTAL_DEV=1 SITE_BASE=/repo/ npm run dev:portal
+ */
+export function getSiteBase() {
+  if (process.env.TALKS_PORTAL_DEV === '1') return ''
+  const raw = process.env.SITE_BASE?.trim() || '/'
+  if (raw === '/') return ''
+  return raw.replace(/\/+$/, '')
+}
+
+/** Valeur `base` VitePress : `/` ou `/mon-projet/` */
+export function vitepressAppBase() {
+  if (process.env.TALKS_PORTAL_DEV === '1') return '/'
+  const raw = process.env.SITE_BASE?.trim()
+  if (!raw || raw === '/') return '/'
+  return raw.endsWith('/') ? raw : `${raw}/`
+}
+
+/** Chemin absolu du site : /slides/foo/ */
+export function sitePath(absolutePath) {
+  const p = absolutePath.startsWith('/') ? absolutePath : `/${absolutePath}`
+  const b = getSiteBase()
+  return b ? `${b}${p}` : p
+}