Story 6-4/6-5: Chat with PDF (done) + PPTX watermark PLG

Story 6-4 — Chat with PDF:
- Feature déjà implémentée (document-qa-overlay.tsx, ingestion, search)
- Marquée done dans sprint-status

Story 6-5 — PPTX Export Watermark (PLG viral loop):
- lib/brainstorm/export-pptx.ts: addWatermark + withWatermark helpers
- lib/ai/tools/pptx.tool.ts: même pattern monkey-patch addSlide
- Watermark 'memento-note.com' 7pt gris bas-droite sur chaque slide
- Zéro modification des 14+ fonctions de slides existantes
- 174 tests passent, aucune erreur TS

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

memento-note/lib/ai/tools/pptx.tool.ts

@@ -105,6 +105,26 @@ const SHAPE_RECT = 'rect' as const
 const SHAPE_ROUND_RECT = 'roundRect' as const
 const SHAPE_OVAL = 'ellipse' as const
 
+/** PLG viral watermark injected on every slide automatically */
+function addWatermark(slide: any) {
+  slide.addText('memento-note.com', {
+    x: 7.0, y: 5.35, w: 2.7, h: 0.2,
+    fontSize: 7, fontFace: 'Arial', color: 'B8B0A8',
+    align: 'right', italic: true,
+  })
+}
+
+/** Wrap pres.addSlide so every new slide gets the Momento watermark automatically */
+function withWatermark(pres: PptxGenJSModule): PptxGenJSModule {
+  const original = pres.addSlide.bind(pres)
+  ;(pres as any).addSlide = (...args: any[]) => {
+    const slide = original(...args)
+    addWatermark(slide)
+    return slide
+  }
+  return pres
+}
+
 function addBadge(s: any, num: number, accent: string) {
   s.addShape(SHAPE_OVAL, {
     x: 9.3, y: 5.1, w: 0.4, h: 0.4,
@@ -978,7 +998,7 @@ async function buildPresentation(spec: PresentationSpec): Promise<PptxGenJSModul
   const style = STYLES[spec.style || 'soft'] || STYLES.soft!
 
   const PptxGenJS = await getPptxGenClass()
-  const pres = new PptxGenJS()
+  const pres = withWatermark(new PptxGenJS())
   pres.title = spec.title
   pres.author = 'Momento'
   pres.subject = spec.title

memento-note/lib/brainstorm/export-pptx.ts

@@ -66,6 +66,29 @@ function truncate(text: string, max: number): string {
   return text.length > max ? text.slice(0, max - 1) + '…' : text
 }
 
+/**
+ * PLG viral watermark — added to every slide automatically via addSlide monkey-patch.
+ * Subtle branding in bottom-right corner to drive organic acquisition.
+ */
+function addWatermark(slide: any) {
+  slide.addText('memento-note.com', {
+    x: 7.0, y: 5.35, w: 2.7, h: 0.2,
+    fontSize: 7, fontFace: 'Arial', color: 'B8B0A8',
+    align: 'right', italic: true,
+  })
+}
+
+/** Wrap pres.addSlide so every new slide gets the Momento watermark automatically */
+function withWatermark(pres: PptxGenJSModule): PptxGenJSModule {
+  const original = pres.addSlide.bind(pres)
+  ;(pres as any).addSlide = (...args: any[]) => {
+    const slide = original(...args)
+    addWatermark(slide)
+    return slide
+  }
+  return pres
+}
+
 // Add a consistent slide background
 function addBg(slide: any) {
   slide.background = { color: T.bg }
@@ -279,7 +302,7 @@ function buildSummarySlide(pres: PptxGenJSModule, session: SessionLike, stats: {
 
 export async function generateBrainstormPptx(session: SessionLike): Promise<{ buffer: Buffer; filename: string }> {
   const PptxGenJS = await getPptxGenClass()
-  const pres = new PptxGenJS()
+  const pres = withWatermark(new PptxGenJS())
 
   pres.layout = 'LAYOUT_WIDE'
   pres.author = 'Momento'