feat: implement agent scheduled execution with cron and time picker

- Add scheduledTime, scheduledDay, timezone fields to Agent schema
- Create calculateNextRun() helper with timezone-aware scheduling
- Add POST /api/cron/agents endpoint for external scheduler
- Calculate nextRun on agent create, update, and after execution
- Add time/day picker in agent form (daily/weekly/monthly)
- Show "Next run" countdown in agent card
- Add i18n keys for schedule UI (FR + EN)

External scheduler (N8N, Vercel Cron) should call /api/cron/agents
every 5-15 min. Requires `prisma db push` to apply schema changes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

memento-note/app/actions/agent-actions.ts

@@ -8,6 +8,7 @@
 import { auth } from '@/auth'
 import { prisma } from '@/lib/prisma'
 import { revalidatePath } from 'next/cache'
+import { calculateNextRun } from '@/lib/agents/schedule'
 
 // --- CRUD ---
 
@@ -24,6 +25,9 @@ export async function createAgent(data: {
   maxSteps?: number
   notifyEmail?: boolean
   includeImages?: boolean
+  scheduledTime?: string
+  scheduledDay?: number
+  timezone?: string
 }) {
   const session = await auth()
   if (!session?.user?.id) {
@@ -45,10 +49,30 @@ export async function createAgent(data: {
         maxSteps: data.maxSteps || 10,
         notifyEmail: data.notifyEmail || false,
         includeImages: data.includeImages || false,
+        scheduledTime: data.scheduledTime || '08:00',
+        scheduledDay: data.scheduledDay ?? null,
+        timezone: data.timezone || null,
         userId: session.user.id,
       }
     })
 
+    // Calculate nextRun for scheduled agents
+    const freq = data.frequency || 'manual'
+    if (freq !== 'manual') {
+      const nextRun = calculateNextRun({
+        frequency: freq,
+        scheduledTime: data.scheduledTime || '08:00',
+        scheduledDay: data.scheduledDay,
+        timezone: data.timezone,
+      })
+      if (nextRun) {
+        await prisma.agent.update({
+          where: { id: agent.id },
+          data: { nextRun },
+        })
+      }
+    }
+
     revalidatePath('/agents')
     return { success: true, agent }
   } catch (error) {
@@ -71,6 +95,9 @@ export async function updateAgent(id: string, data: {
   maxSteps?: number
   notifyEmail?: boolean
   includeImages?: boolean
+  scheduledTime?: string
+  scheduledDay?: number | null
+  timezone?: string
 }) {
   const session = await auth()
   if (!session?.user?.id) {
@@ -97,6 +124,31 @@ export async function updateAgent(id: string, data: {
     if (data.maxSteps !== undefined) updateData.maxSteps = data.maxSteps
     if (data.notifyEmail !== undefined) updateData.notifyEmail = data.notifyEmail
     if (data.includeImages !== undefined) updateData.includeImages = data.includeImages
+    if (data.scheduledTime !== undefined) updateData.scheduledTime = data.scheduledTime
+    if (data.scheduledDay !== undefined) updateData.scheduledDay = data.scheduledDay
+    if (data.timezone !== undefined) updateData.timezone = data.timezone
+
+    // Recalculate nextRun when scheduling fields change
+    const shouldRecalcNextRun =
+      data.frequency !== undefined ||
+      data.scheduledTime !== undefined ||
+      data.scheduledDay !== undefined ||
+      data.timezone !== undefined
+
+    if (shouldRecalcNextRun) {
+      const freq = data.frequency || existing.frequency
+      if (freq === 'manual') {
+        updateData.nextRun = null
+      } else {
+        const nextRun = calculateNextRun({
+          frequency: freq,
+          scheduledTime: data.scheduledTime || existing.scheduledTime || '08:00',
+          scheduledDay: data.scheduledDay ?? existing.scheduledDay,
+          timezone: data.timezone || existing.timezone,
+        })
+        updateData.nextRun = nextRun
+      }
+    }
 
     const agent = await prisma.agent.update({
       where: { id },