feat: workspaces system — create, select, rename, delete workspaces

- DB: pages.workspace_id column linking pages to workspaces table
- /workspaces: list, create, rename, delete workspaces page
- API: GET/POST/PUT/DELETE /api/workspaces + POST select
- Session: flowdeck_workspace cookie for active workspace tracking
- Sidebar: Workspace section shows active workspace name + page tree
- Local workspace APIs filter by active workspace_id
- Home redirects non-Gitea users to /workspaces

app/templates/base.html

@@ -85,16 +85,22 @@
       <div class="sidebar-section-header" @click="toggleSection('workspace')">
         <div class="sidebar-section-title">
           <span class="chevron" :class="{ open: sectionsOpen.workspace }" x-text="sectionsOpen.workspace ? '▼' : '▶'"></span>
-          <span>📁 Workspace</span>
+          <span>📁 {{ workspace_name or 'Workspace' }}</span>
         </div>
         <div class="sidebar-section-actions">
-          <button class="section-action-btn" title="New File" @click.stop="newPage('Private')">+</button>
+          <button class="section-action-btn" title="New Page" @click.stop="newPageInWorkspace()">+</button>
         </div>
       </div>
       <div class="sidebar-section-items" x-show="sectionsOpen.workspace" x-transition>
         <ul class="sidebar-items" data-section="workspace">
-          <li class="sidebar-item" onclick="window.location='/local-workspace'">
-            <span class="page-icon">📁</span><span class="page-name">My Workspace</span>
+          {% for page in workspace_pages %}
+            {{ render_tree_item(page) }}
+          {% endfor %}
+          {% if not workspace_pages %}
+          <li class="sidebar-item empty-hint"><span class="page-icon">📄</span><span class="page-name text-dim">No pages yet</span></li>
+          {% endif %}
+          <li class="sidebar-item" style="margin-top:4px;border-top:1px solid var(--border);padding-top:8px;" onclick="window.location='/workspaces'">
+            <span class="page-icon">⚙</span><span class="page-name text-dim">Manage Workspaces</span>
           </li>
         </ul>
       </div>