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>

web/src/components/AppSidebar.vue

@@ -0,0 +1,109 @@
+<script setup lang="ts">
+import { computed, onMounted, ref } from 'vue'
+import { RouterLink, useRouter } from 'vue-router'
+import { ApiError } from '../lib/api'
+import { MAX_PROJECTS, useProjectsStore } from '../stores/projects'
+
+const projects = useProjectsStore()
+const router = useRouter()
+
+const title = ref('')
+const createError = ref<ApiError | null>(null)
+const submitting = ref(false)
+const loadError = ref<string | null>(null)
+
+const atLimit = computed(() => projects.projects.length >= MAX_PROJECTS)
+
+onMounted(() => {
+  if (!projects.loaded) void load()
+})
+
+async function load() {
+  loadError.value = null
+  try {
+    await projects.fetchProjects()
+  } catch (e) {
+    loadError.value = e instanceof ApiError ? e.message : 'Could not load your projects.'
+  }
+}
+
+async function onCreate() {
+  submitting.value = true
+  createError.value = null
+  try {
+    const project = await projects.createProject(title.value)
+    title.value = ''
+    await router.push({ name: 'project', params: { id: project.id } })
+  } catch (e) {
+    createError.value = e instanceof ApiError ? e : new ApiError('Could not create the project.', 0)
+  } finally {
+    submitting.value = false
+  }
+}
+</script>
+
+<template>
+  <aside class="sidebar">
+    <nav class="sidebar__nav">
+      <RouterLink :to="{ name: 'dashboard' }" class="sidebar__link" active-class="sidebar__link--active">
+        <svg class="sidebar__icon" viewBox="0 0 16 16" aria-hidden="true">
+          <rect x="1" y="1" width="6" height="6" rx="1.2" />
+          <rect x="9" y="1" width="6" height="6" rx="1.2" />
+          <rect x="1" y="9" width="6" height="6" rx="1.2" />
+          <rect x="9" y="9" width="6" height="6" rx="1.2" />
+        </svg>
+        <span>Dashboard</span>
+      </RouterLink>
+    </nav>
+
+    <hr class="sidebar__divider" />
+
+    <p class="sidebar__heading">Projects</p>
+
+    <p v-if="loadError" class="sidebar__note form-error">{{ loadError }}</p>
+    <p v-else-if="projects.loading && !projects.loaded" class="sidebar__note muted">Loading…</p>
+    <p v-else-if="projects.projects.length === 0" class="sidebar__note muted">No projects yet.</p>
+
+    <nav v-else class="sidebar__nav sidebar__projects">
+      <RouterLink
+        v-for="project in projects.projects"
+        :key="project.id"
+        :to="{ name: 'project', params: { id: project.id } }"
+        class="sidebar__link sidebar__link--project"
+        active-class="sidebar__link--active"
+      >
+        <svg class="sidebar__icon" viewBox="0 0 16 16" aria-hidden="true">
+          <rect x="1" y="2" width="3.5" height="12" rx="1" />
+          <rect x="6.25" y="2" width="3.5" height="9" rx="1" />
+          <rect x="11.5" y="2" width="3.5" height="6" rx="1" />
+        </svg>
+        <span class="sidebar__link-text">{{ project.title }}</span>
+      </RouterLink>
+    </nav>
+
+    <form class="sidebar__form" @submit.prevent="onCreate">
+      <input
+        v-model="title"
+        type="text"
+        maxlength="255"
+        required
+        :disabled="atLimit"
+        placeholder="New project"
+        aria-label="New project title"
+      />
+      <small v-if="createError?.fieldError('title')" class="field-error">
+        {{ createError.fieldError('title') }}
+      </small>
+      <small
+        v-else-if="createError && Object.keys(createError.details).length === 0"
+        class="field-error"
+      >
+        {{ createError.message }}
+      </small>
+      <button type="submit" :disabled="submitting || atLimit">
+        {{ submitting ? 'Creating…' : 'Add project' }}
+      </button>
+      <small v-if="atLimit" class="hint">Limit of {{ MAX_PROJECTS }} projects reached.</small>
+    </form>
+  </aside>
+</template>