fix: 5 bugs critiques de l'éditeur (Phase 1 audit)

1. replaceAll (Find & Replace) — une seule transaction ProseMirror
   au lieu d'un forEach cassé. Tous les matchs sont maintenant remplacés.

2. Link Preview unwrap — deleteNode() au lieu de clearer les attrs
   qui laissaient un nœud fantôme invisible dans le document.

3. Conversion Markdown → richtext — breaks: true dans marked.parse()
   Les simple newlines sont maintenant convertis en <br>.
   + préserve les blocs custom (toggle, callout, math, columns,
   outline, link-preview) en commentaires HTML lors de l'export MD.

4. emitNoteChange exercices — shape corrigée (type:'created' attend
   un objet Note, pas noteId/notebookId séparés).

5. Raccourcis clavier sans conflit :
   Cmd+Shift+C → Cmd+Alt+C (callout, avant: copier)
   Cmd+Shift+O → Cmd+Alt+O (outline, avant: historique/signets)
   Cmd+Shift+L → Cmd+Alt+L (colonnes, avant: lock screen macOS)

memento-note/locales/en.json

@@ -1453,6 +1453,7 @@
       "dashboard": "Dashboard",
       "users": "Users",
       "aiManagement": "AI Management",
+      "billing": "Billing & Quotas",
       "published": "Published pages",
       "chat": "AI Chat",
       "lab": "The Lab (Ideas)",
@@ -1481,6 +1482,40 @@
       "testSearch": "Test web search"
     },
     "settingsDescription": "Configure application-wide settings",
+    "billing": {
+      "title": "Billing & Quotas",
+      "description": "Manage subscription tiers, AI quotas, and Stripe business settings without redeploying.",
+      "stripeConfigTitle": "Stripe business config",
+      "stripeConfigDescription": "Price IDs and billing toggle. Secret keys stay in server environment only.",
+      "enableBilling": "Enable billing UI and checkout",
+      "STRIPE_PRICE_PRO_MONTHLY": "Pro — monthly price ID",
+      "STRIPE_PRICE_PRO_ANNUAL": "Pro — annual price ID",
+      "STRIPE_PRICE_BUSINESS_MONTHLY": "Business — monthly price ID",
+      "STRIPE_PRICE_BUSINESS_ANNUAL": "Business — annual price ID",
+      "secretsNote": "STRIPE_SECRET_KEY and STRIPE_WEBHOOK_SECRET must remain in Docker/env secrets — never stored here.",
+      "saveConfig": "Save billing config",
+      "configSaved": "Billing configuration saved",
+      "configFailed": "Failed to save billing configuration",
+      "limitsTitle": "Tier quotas",
+      "limitsDescription": "Monthly request limits per feature. Changes apply within ~60 seconds.",
+      "feature": "Feature",
+      "mode": "Access",
+      "monthlyLimit": "Monthly limit",
+      "actions": "Actions",
+      "modeUnavailable": "Not available",
+      "modeLimited": "Limited",
+      "modeUnlimited": "Unlimited",
+      "saveLimit": "Save",
+      "limitSaved": "Quota updated",
+      "limitFailed": "Failed to update quota",
+      "usageTitle": "Usage overview",
+      "usagePeriod": "Period {period}",
+      "lastSync": "Last sync {date}",
+      "notSynced": "Not synced yet (cron /api/cron/sync-usage)",
+      "byFeature": "By feature (PostgreSQL)",
+      "topUsers": "Top users",
+      "noUsageData": "No usage data for this period yet"
+    },
     "dashboard": {
       "title": "Dashboard",
       "description": "Overview of your application metrics",
@@ -3072,6 +3107,7 @@
   },
   "billing": {
     "title": "Billing",
+    "disabledByAdmin": "Billing and upgrades are currently disabled. Contact your administrator if you need access.",
     "currentPlan": "Current Plan",
     "upgradePlan": "Upgrade Plan",
     "manageBilling": "Manage Billing",