feat: Refonte UI Notion-complete — sidebar, topbar, multi-vues, dark mode

- Layout 3 zones (sidebar 240px + topbar 44px + contenu)
- Sidebar: sections hiérarchiques, hover states, menu contextuel
- CSS design system Notion: #191919/#222/#333, Inter, coins 4-6px
- Vues: Kanban (groupes+colonnes), Dashboard Notion-style
- Templates: base.html refondu, card.html partial, board.html v2
- Backend: données sidebar + board Notion (groups/cards)
- Docs: ROADMAP v0.4→v1.0, WORKLOAD.md, README
- Backward compatible: conserve _issue_column pour api.py
- Images de référence + resized (analyse 2026-07-08)

app/templates/card.html

@@ -0,0 +1,28 @@
+{# Card partial for Kanban board — Notion style #}
+<div class="kanban-card card-status-{{ card.status }}"
+     data-card-id="{{ card.id }}"
+     data-card-status="{{ card.status }}"
+     draggable="false">
+  <div class="card-header">
+    <span class="card-icon">{{ card.icon }}</span>
+    <span class="card-title">{{ card.title }}</span>
+  </div>
+  <div class="card-meta">
+    {% if card.assignee %}
+    <div class="card-assignee">
+      <div class="card-avatar" title="{{ card.assignee }}">{{ card.assignee[0] }}</div>
+      <span>{{ card.assignee }}</span>
+    </div>
+    {% endif %}
+    {% if card.tag %}
+    <span class="card-tag" style="background: {{ card.tag_color }}20; color: {{ card.tag_color }};">
+      {{ card.tag }}
+    </span>
+    {% endif %}
+    {% if card.due_date %}
+    <div class="card-date">
+      <span>📅</span> {{ card.due_date }}
+    </div>
+    {% endif %}
+  </div>
+</div>