feat(4-5/4-6): audit logging + zero-data-retention headers

Audit Logging (story 4-6):
- Nouveau modèle AuditLog (userId, action, resource, metadata, ip, createdAt)
- Migration 20260529143000_add_audit_log appliquée
- lib/audit-log.ts : logAuditEvent (fire-and-forget) + logAuditEventAsync + getClientIp
- auth.ts : LOG LOGIN / LOGOUT / USER_CREATED sur chaque event NextAuth
- /api/chat : log AI_REQUEST avec tokens + byok flag dans onFinish
- /api/agents/run-for-note : log AI_REQUEST avec featureKey + noteId

Zero-data-retention (story 4-5):
- OpenAI provider : header OpenAI-No-Training: 1
- Anthropic provider : header Anthropic-No-Train: 1
- DeepSeek provider : header X-No-Train: 1

sprint-status: 4-5 et 4-6 → done

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

memento-note/app/api/agents/run-for-note/route.ts

@@ -2,6 +2,7 @@ import { NextRequest, NextResponse } from 'next/server'
 import { auth } from '@/auth'
 import { prisma } from '@/lib/prisma'
 import { checkEntitlementOrThrow, QuotaExceededError, incrementUsageAsync } from '@/lib/entitlements'
+import { logAuditEvent, getClientIp } from '@/lib/audit-log'
 
 type GenerateType = 'slide-generator' | 'excalidraw-generator'
 
@@ -107,6 +108,14 @@ export async function POST(req: NextRequest) {
     .then(({ executeAgent }) => executeAgent(agent.id, userId))
     .catch(err => console.error('[run-for-note] Background agent error:', err))
 
+  logAuditEvent({
+    userId,
+    action: 'AI_REQUEST',
+    resource: featureKey,
+    metadata: { agentId: agent.id, noteId, featureKey },
+    ip: getClientIp(req),
+  })
+
   return NextResponse.json({ success: true, agentId: agent.id, status: 'running' })
 }
 

memento-note/app/api/chat/route.ts

@@ -12,6 +12,7 @@ import { checkEntitlementOrThrow, QuotaExceededError, incrementUsageAsync } from
 import { trackFeatureUsage } from '@/lib/usage-tracker'
 import { readFile } from 'fs/promises'
 import path from 'path'
+import { logAuditEvent, getClientIp } from '@/lib/audit-log'
 
 export const maxDuration = 60
 
@@ -433,6 +434,13 @@ Focus ONLY on this note unless asked otherwise.`
             trackFeatureUsage(userId, 'chat', final.usage?.totalTokens ?? 0)
             incrementUsageAsync(userId, 'chat')
           }
+          logAuditEvent({
+            userId,
+            action: 'AI_REQUEST',
+            resource: 'chat',
+            metadata: { tokens: final.usage?.totalTokens, byok: usedByok },
+            ip: getClientIp(req),
+          })
         },
       }),
   )