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/dev-portal.mjs

@@ -0,0 +1,40 @@
+#!/usr/bin/env node
+/**
+ * npm run dev:portal — sync + VitePress dev avec base=/ (ignore SITE_BASE sauf SKIP_PORTAL_DEV=1).
+ */
+import path from 'node:path'
+import { fileURLToPath } from 'node:url'
+import { spawn, execFileSync } from 'node:child_process'
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url))
+const root = path.resolve(__dirname, '..')
+const runEnv =
+  process.env.SKIP_PORTAL_DEV === '1'
+    ? process.env
+    : { ...process.env, TALKS_PORTAL_DEV: '1' }
+
+execFileSync(process.execPath, [path.join(root, 'tools', 'sync-portal.mjs')], {
+  stdio: 'inherit',
+  cwd: root,
+  env: runEnv,
+})
+
+const vitepressBin = path.join(root, 'node_modules', '.bin', 'vitepress')
+const child = spawn(vitepressBin, ['dev', 'portal'], {
+  cwd: root,
+  stdio: 'inherit',
+  env: runEnv,
+  shell: process.platform === 'win32',
+})
+
+function die() {
+  try {
+    child.kill('SIGTERM')
+  } catch {
+    /* ignore */
+  }
+  process.exit(0)
+}
+process.on('SIGINT', die)
+process.on('SIGTERM', die)
+child.on('exit', (code) => process.exit(code ?? 0))