feat(graph): Phase 3 — type filter, export PNG, fullscreen, focus node

- Type filter checkboxes (dossier, .md, autre) in legend
- Export PNG button (canvas.toDataURL)
- Fullscreen button (Fullscreen API)
- Focus node function (center on specific node)
- Filter applied during _draw() to skip hidden nodes

frontend/index.html

@@ -717,6 +717,12 @@
           <button class="editor-btn" id="graph-reset" title="Réinitialiser la vue" aria-label="Réinitialiser">
             <i data-lucide="maximize" style="width:16px;height:16px"></i>
           </button>
+          <button class="editor-btn" id="graph-export" title="Exporter en PNG" aria-label="Export PNG">
+            <i data-lucide="download" style="width:16px;height:16px"></i>
+          </button>
+          <button class="editor-btn" id="graph-fullscreen" title="Plein écran" aria-label="Plein écran">
+            <i data-lucide="expand" style="width:16px;height:16px"></i>
+          </button>
           <button class="editor-btn" id="graph-close" title="Fermer" aria-label="Fermer">
             <i data-lucide="x" style="width:16px;height:16px"></i>
           </button>
@@ -725,10 +731,11 @@
       <div class="editor-body" style="flex:1;overflow:hidden;position:relative;padding:0">
         <canvas id="graph-canvas" style="width:100%;height:100%;cursor:grab"></canvas>
         <div id="graph-tooltip" style="display:none;position:absolute;pointer-events:none;background:var(--bg-primary);border:1px solid var(--border-color);border-radius:6px;padding:6px 10px;font-size:0.75rem;color:var(--text-primary);max-width:250px;z-index:10;box-shadow:0 2px 8px rgba(0,0,0,0.3)"></div>
-        <div id="graph-legend" style="position:absolute;bottom:12px;left:12px;display:flex;gap:16px;font-size:0.7rem;color:var(--text-muted);background:var(--bg-primary);padding:6px 12px;border-radius:6px;border:1px solid var(--border-color)">
-          <span>🟦 Dossier</span>
-          <span>🟩 Fichier .md</span>
-          <span>⬜ Autre fichier</span>
+        <div id="graph-legend" style="position:absolute;bottom:12px;left:12px;display:flex;gap:12px;font-size:0.7rem;color:var(--text-muted);background:var(--bg-primary);padding:6px 12px;border-radius:6px;border:1px solid var(--border-color);align-items:center;flex-wrap:wrap">
+          <label style="cursor:pointer;display:flex;align-items:center;gap:3px"><input type="checkbox" id="graph-filter-dir" checked> 🟦 Dossier</label>
+          <label style="cursor:pointer;display:flex;align-items:center;gap:3px"><input type="checkbox" id="graph-filter-md" checked> 🟩 .md</label>
+          <label style="cursor:pointer;display:flex;align-items:center;gap:3px"><input type="checkbox" id="graph-filter-other" checked> ⬜ Autre</label>
+          <span style="color:var(--text-muted);margin:0 4px">│</span>
           <span style="color:var(--text-muted)">── Parent</span>
           <span style="color:var(--accent-color,#2563eb)">┅┅ Wikilink</span>
           <span style="color:#e74c3c">← Backlink</span>