feat(agents): refonte complète slide-generator + excalidraw-generator

Slide generator (generate_pptx):
- Pivot vers génération PowerPoint natif (pptxgenjs) au lieu de Reveal.js HTML
- 4 nouveaux layouts diagramme : timeline, process, comparison, metrics
- 2 nouveaux layouts image : image-content (texte + image), image-full (plein cadre)
- Redesign visuel de tous les layouts (cover split, section full-bleed, header band)
- Palettes corrigées : bg blanc sur toutes les palettes, contrastes réels
- fit:shrink systématique sur tous les textes pour éviter les débordements
- Extraction automatique des images des notes (Markdown/HTML) et injection dans le prompt IA
- Prompt IA renforcé : impose "style" et "theme" explicitement dans le JSON, impose ≥2 layouts diagramme
- Fix overlap timeline : zones de texte calculées sans collision avec les cercles
- Notification agent mise à jour : bouton download .pptx au lieu d'ouvrir HTML

Excalidraw generator:
- Layout Dagre/ELK pour graphes auto-positionnés
- Styles visuels : coloré, austère, sketch-plus (Virgil font)
- Zones/containers pour architecture-cloud
- Sanitisation du graphe et métriques de qualité de layout

Co-authored-by: Cursor <cursoragent@cursor.com>

memento-note/app/api/canvas/download/route.ts

@@ -0,0 +1,47 @@
+import { NextRequest, NextResponse } from 'next/server'
+import { prisma } from '@/lib/prisma'
+import { auth } from '@/auth'
+
+export async function GET(req: NextRequest) {
+  try {
+    const session = await auth()
+    if (!session?.user?.id) return NextResponse.json({ error: 'Unauthorized' }, { status: 401 })
+
+    const canvasId = req.nextUrl.searchParams.get('id')
+    if (!canvasId) return NextResponse.json({ error: 'Missing id' }, { status: 400 })
+
+    const canvas = await prisma.canvas.findUnique({
+      where: { id: canvasId, userId: session.user.id },
+    })
+    if (!canvas) return NextResponse.json({ error: 'Not found' }, { status: 404 })
+
+    let parsed: any
+    try { parsed = JSON.parse(canvas.data) } catch {
+      return NextResponse.json({ error: 'Invalid data' }, { status: 500 })
+    }
+
+    if (parsed.type !== 'pptx' || !parsed.base64) {
+      return NextResponse.json({ error: 'Not a PPTX canvas' }, { status: 400 })
+    }
+
+    const byteChars = atob(parsed.base64)
+    const bytes = new Uint8Array(byteChars.length)
+    for (let i = 0; i < byteChars.length; i++) bytes[i] = byteChars.charCodeAt(i)
+
+    const filename = parsed.filename || `${canvas.name.replace(/[^a-zA-Z0-9]/g, '_')}.pptx`
+
+    // Auto-delete after serving
+    await prisma.canvas.delete({ where: { id: canvasId } })
+
+    return new NextResponse(bytes, {
+      headers: {
+        'Content-Type': 'application/vnd.openxmlformats-officedocument.presentationml.presentation',
+        'Content-Disposition': `attachment; filename="${filename}"`,
+        'Content-Length': String(bytes.length),
+      },
+    })
+  } catch (error) {
+    console.error('[Canvas Download]', error)
+    return NextResponse.json({ error: 'Internal Server Error' }, { status: 500 })
+  }
+}

memento-note/app/api/canvas/slides/route.ts

@@ -0,0 +1,70 @@
+import { NextRequest } from 'next/server'
+import { prisma } from '@/lib/prisma'
+
+export async function GET(req: NextRequest) {
+  try {
+    const canvasId = req.nextUrl.searchParams.get('id')
+    console.log('[Slides API] Request for id:', canvasId)
+
+    if (!canvasId) {
+      console.log('[Slides API] ERROR: Missing id')
+      return new Response(JSON.stringify({ error: 'Missing id' }), {
+        status: 400,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    }
+
+    const canvas = await prisma.canvas.findUnique({
+      where: { id: canvasId },
+    })
+
+    if (!canvas) {
+      console.log('[Slides API] ERROR: Canvas not found for id:', canvasId)
+      return new Response(JSON.stringify({ error: 'Not found' }), {
+        status: 404,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    }
+
+    console.log('[Slides API] Canvas found:', canvas.name, '| data length:', canvas.data?.length)
+    console.log('[Slides API] Raw data start:', canvas.data?.substring(0, 200))
+
+    let parsed: any
+    try {
+      parsed = JSON.parse(canvas.data)
+    } catch (parseErr) {
+      console.log('[Slides API] ERROR: JSON parse failed:', parseErr)
+      return new Response(JSON.stringify({ error: 'Invalid data' }), {
+        status: 500,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    }
+
+    console.log('[Slides API] Parsed type:', parsed.type, '| has html:', !!parsed.html, '| html length:', parsed.html?.length)
+    console.log('[Slides API] HTML start:', parsed.html?.substring(0, 150))
+
+    if (parsed.type !== 'slides' || !parsed.html) {
+      console.log('[Slides API] ERROR: Not a slides canvas. type:', parsed.type, 'html exists:', !!parsed.html)
+      return new Response(JSON.stringify({ error: 'Not a slides canvas' }), {
+        status: 400,
+        headers: { 'Content-Type': 'application/json' },
+      })
+    }
+
+    console.log('[Slides API] SUCCESS: Returning HTML, length:', parsed.html.length)
+
+    return new Response(parsed.html, {
+      status: 200,
+      headers: {
+        'Content-Type': 'text/html; charset=utf-8',
+        'Cache-Control': 'no-cache',
+      },
+    })
+  } catch (error) {
+    console.error('[Slides API] FATAL:', error)
+    return new Response(JSON.stringify({ error: 'Internal Server Error' }), {
+      status: 500,
+      headers: { 'Content-Type': 'application/json' },
+    })
+  }
+}