Add a persistent left sidebar to the signed-in layout

App.vue now renders a left AppSidebar beside the routed view for any
requiresAuth page, staying mounted as you move between the dashboard and
projects. The sidebar has a Dashboard link (icon), a divider, the project list
(each an icon link, current page highlighted via RouterLink active-class), and a
compact new-project form that jumps to the created project.

- New /dashboard route + DashboardView ("under construction"); / and unknown
  paths redirect there. HomeView removed -- its project list and form moved into
  the sidebar.
- <RouterView :key="route.path"> so navigating project -> project via the
  sidebar remounts and reloads instead of reusing the instance.
- Signed-out routes (login/register/verify-email) render without the sidebar.

Icons are inline SVG -- no new dependency.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -18,6 +18,7 @@ Each user owns **projects**, and each project holds ordered **cards**.
 | 8 | Passwordless login — magic-link by default, password login behind a toggle | ✅ done |
 | 9 | Per-project card statuses ("To do" / "Doing" / "Done"); status chip, new cards start with none | ✅ done |
 | 10 | Project view — full-width, tabbed: alphabetical "All tasks" list + "Kanban" board, per-column drag ordering | ✅ done |
+| 11 | Persistent left sidebar — Dashboard link + project list/new-project form; `/` → dashboard placeholder | ✅ done |
 
 Registration signs the user in immediately and emails a magic link that verifies
 the address; `user.email_verified` stays `false` until the link is opened. See