Sprint 4 : decisions et mandats -- workflow complet + vote integration

Backend: 7 nouveaux endpoints (advance, assign, revoke, create-vote-session),
services enrichis avec creation de sessions de vote, assignation de mandataire
et revocation. 35 nouveaux tests (104 total). Frontend: store mandates, page
cadrage decisions, detail mandats, composants DecisionWorkflow, DecisionCadrage,
DecisionCard, MandateTimeline, MandateCard. Documentation mise a jour.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/app/pages/decisions/new.vue

@@ -0,0 +1,72 @@
+<script setup lang="ts">
+import type { DecisionCreate } from '~/stores/decisions'
+
+const decisions = useDecisionsStore()
+
+const formData = ref<DecisionCreate>({
+  title: '',
+  description: '',
+  context: '',
+  decision_type: 'other',
+  voting_protocol_id: null,
+})
+
+const submitting = ref(false)
+
+async function onSubmit() {
+  submitting.value = true
+  try {
+    const decision = await decisions.create(formData.value)
+    if (decision) {
+      navigateTo(`/decisions/${decision.id}`)
+    }
+  } catch {
+    // Error is handled by the store
+  } finally {
+    submitting.value = false
+  }
+}
+</script>
+
+<template>
+  <div class="space-y-6">
+    <!-- Back link -->
+    <div>
+      <UButton
+        to="/decisions"
+        variant="ghost"
+        color="neutral"
+        icon="i-lucide-arrow-left"
+        label="Retour aux decisions"
+        size="sm"
+      />
+    </div>
+
+    <!-- Header -->
+    <div>
+      <h1 class="text-2xl font-bold text-gray-900 dark:text-white">
+        Nouvelle decision
+      </h1>
+      <p class="mt-1 text-sm text-gray-600 dark:text-gray-400">
+        Cadrage d'un nouveau processus de decision collectif
+      </p>
+    </div>
+
+    <!-- Error -->
+    <UCard v-if="decisions.error">
+      <div class="flex items-center gap-3 text-red-500">
+        <UIcon name="i-lucide-alert-circle" class="text-xl" />
+        <p>{{ decisions.error }}</p>
+      </div>
+    </UCard>
+
+    <!-- Form -->
+    <UCard>
+      <DecisionsDecisionCadrage
+        v-model="formData"
+        :submitting="submitting"
+        @submit="onSubmit"
+      />
+    </UCard>
+  </div>
+</template>