feat(editor): v4.8.0 Bloc Tableau simple (edition Notion via /table)

- Bloc table editable: slash /table, cellules contenteditable, auto-save
- Colonnes: poignee par colonne -> Insert left/right, Duplicate, Clear, Delete
- Lignes: + Row (bas) + menu contextuel -> Insert above/below, Dup, Clear, Del
- md2b importe les tableaux GFM pipe en bloc table (au lieu de paragraphes)
- Roundtrip markdown (JS + export Python MD/HTML/PDF)
- CSS .ftable-editor + menu flottant (app.css?v=4.8.0)
- VERSION/CHANGELOG/ROADMAP bump 4.8.0 (Collaboration -> v4.9.0, Agent -> v4.10.0)

app/templates/base.html

@@ -5,7 +5,7 @@
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <title>FlowDeck — {% block title_prefix %}Home{% endblock %}</title>
   <link rel="icon" type="image/svg+xml" href="/static/favicon.svg">
-  <link rel="stylesheet" href="/static/css/app.css?v=4.7.1">
+  <link rel="stylesheet" href="/static/css/app.css?v=4.8.0">
   <link rel="stylesheet" href="/static/css/katex.min.css?v=0.16.11">
   <style>
     /* ── Mobile responsive (v4.0.2) ── */