feat(insights): UX gap closure — i18n, network graph, recalc panel, toasts

Bugs fixes:
- network-graph.tsx: 2 strings hardcoded FR → props i18n (untitledLabel, resetFocusLabel)
- Panneau recalcul: clés i18n réutilisées avec mauvais sens → nouvelles clés recalcSystem.*
- 13 locales: section insightsView.* complète (67 clés × 13 = 871 traductions)

UX features:
- Hint /insights ≠ /graph (semanticGraphLegend + lien vers /graph)
- Toasts succès/échec/zéro-clusters après analyse (analysisSuccess/Failed/NoClusters)
- État vide différencié: emptyNeedMoreNotes si < 10 notes
- Tips contextuels sections Bridge Notes et Suggestions

Sprint:
- 4 epics marqués done (3,4,5,6 — toutes stories terminées)
- sprint-status.yaml last_updated corrigé

memento-note/locales/en.json

@@ -3525,7 +3525,14 @@
     "tipSuggestions": "These themes have no note linking them yet. AI proposes a starting idea. Click 'Create bridge note' to write it and open it in the editor.",
     "tipSuggestionsAction": "Click 'Create bridge note' to write the note and open it immediately.",
     "tipIsolated": "These themes are isolated: no note connects them to the others. Maybe you're exploring a fragile idea? One synthesis note would be enough to create the link.",
-    "tipIsolatedAction": "These themes have no note connecting them to the rest of your thinking."
+    "tipIsolatedAction": "These themes have no note connecting them to the rest of your thinking.",
+    "recalcSystem": {
+      "title": "Recalculation system",
+      "statusSynced": "Synced",
+      "scheduledCron": "Scheduled",
+      "lastSync": "Last sync"
+    },
+    "resetFocus": "Reset focus"
   },
   "consent": {
     "banner": {