Make Explore and Kanban real routes, not tab state

/projects/:id (name "project") is now Explore; /projects/:id/kanban
(name "project-kanban") is Kanban. ProjectView.vue becomes a layout:
header + sub-nav, loading the project and its cards (both children
need the cards list) and rendering the active one via <RouterView>.
ProjectExploreView.vue and ProjectKanbanView.vue hold what used to be
each tab's own template/logic; Kanban additionally loads its own
statuses, since Explore has no use for them.

The sub-nav is now RouterLinks (active state matched on route.name),
not buttons toggling local state.

App.vue: the top-level <RouterView> was keyed by the full route path
to force a fresh instance per project/card id -- with Explore/Kanban
now separate paths under one layout, that would also remount the
layout (and re-fetch the project) on every tab switch. Keyed by the
matched route's top-level path + params instead, which is the same
value for both of a project's child routes.

AppSidebar: the project switcher and the inbox-drag refresh both used
to check route.name === 'project' for "this project is open" -- fixed
to cover both routes for the switcher, and narrowed to
'project-kanban' specifically for the inbox-drag refresh, since Kanban
is the only route with a draggable list a card could have moved
to/from.

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

web/src/views/ProjectExploreView.vue

@@ -0,0 +1,88 @@
+<script setup lang="ts">
+import { computed, ref } from 'vue'
+import CardRow from '../components/CardRow.vue'
+import { ApiError } from '../lib/api'
+import { useCardsStore } from '../stores/cards'
+
+// The project's cards, flat and sorted by name -- ProjectView (the parent
+// layout) has already loaded them into this store, keyed to the current
+// project, so there's nothing to fetch here.
+const cards = useCardsStore()
+
+const actionError = ref<string | null>(null)
+const newText = ref('')
+const submitting = ref(false)
+
+const summary = computed(() => {
+  const total = cards.cards.length
+  if (total === 0) return 'No cards yet.'
+  return `${total} card${total === 1 ? '' : 's'}.`
+})
+
+// No manual order here -- sort by name, case-insensitively.
+const sortedCards = computed(() =>
+  [...cards.cards].sort((a, b) => a.text.localeCompare(b.text, undefined, { sensitivity: 'base' })),
+)
+
+/** Run a store mutation, surfacing failures and resyncing from the server. */
+async function run(op: Promise<unknown>) {
+  actionError.value = null
+  try {
+    await op
+  } catch (e) {
+    actionError.value = e instanceof ApiError ? e.message : 'Something went wrong.'
+    if (cards.projectId !== null) await cards.load(cards.projectId)
+  }
+}
+
+async function onCreate() {
+  submitting.value = true
+  actionError.value = null
+  try {
+    await cards.add(newText.value)
+    newText.value = ''
+  } catch (e) {
+    actionError.value = e instanceof ApiError ? e.message : 'Could not add the card.'
+  } finally {
+    submitting.value = false
+  }
+}
+</script>
+
+<template>
+  <div>
+    <p v-if="actionError" class="form-error">{{ actionError }}</p>
+
+    <p class="muted">{{ summary }}</p>
+
+    <p v-if="cards.loading && !cards.loaded" class="muted">Loading…</p>
+
+    <ul v-else-if="sortedCards.length" class="cards">
+      <CardRow
+        v-for="card in sortedCards"
+        :key="card.id"
+        :card="card"
+        @delete="run(cards.remove(card))"
+      />
+    </ul>
+
+    <form class="kanban__new form--new-card" @submit.prevent="onCreate">
+      <input
+        v-model="newText"
+        class="field field--compact"
+        type="text"
+        maxlength="1000"
+        required
+        placeholder="New card"
+        aria-label="New card"
+      />
+      <button
+        type="submit"
+        class="btn-icon"
+        :disabled="submitting"
+        :title="submitting ? 'Adding…' : 'Add card'"
+        :aria-label="submitting ? 'Adding…' : 'Add card'"
+      >+</button>
+    </form>
+  </div>
+</template>