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

docs/sprint-status.yaml

@@ -35,14 +35,14 @@
 # - Dev moves story to 'review', then runs code-review (fresh context, different LLM recommended)
 
 generated: 2026-05-14T16:06:50Z
-last_updated: 2026-05-23T20:03:48Z
+last_updated: 2026-06-28T16:45:00Z
 project: Memento
 project_key: NOKEY
 tracking_system: file-system
 story_location: docs
 
 development_status:
-  epic-3: in-progress
+  epic-3: done
   3-1-freemium-quota-tracking: done
   3-2-custom-llm-router: done
   3-3-smart-routing-fallback: done
@@ -50,7 +50,7 @@ development_status:
   3-5-secure-byok-management: done
   3-6-stripe-subscription-tiers: done
   epic-3-retrospective: optional
-  epic-4: in-progress
+  epic-4: done
   4-1-gdpr-cookie-consent: done
   4-2-gdpr-right-to-be-forgotten: done
   4-3-data-portability: done
@@ -58,11 +58,12 @@ development_status:
   4-5-eu-data-residency: done
   4-6-sso-saml-audit-logging: done
   epic-4-retrospective: optional
-  epic-5: in-progress
+  epic-5: done
   5-1-nextgen-editor: done
+  epic-5-retrospective: optional
 
   # Epic 6 — Croissance & Activation (PLG) — ajouté 2026-05-29
-  epic-6: in-progress
+  epic-6: done
   6-1-onboarding-activation: done             # story-onboarding-activation.md
   6-2-markdown-roundtrip: done        # brief-markdown-roundtrip.md
   6-3-brainstorm-canvas-finalize: done        # story: 6-3-brainstorm-canvas-finalize.md