Tint the kanban inbox column lighter than the status columns

New --inbox-bg token (light and dark) applied via .kanban__col--inbox so the
inbox reads as distinct from "To do" / "Doing" / "Done".

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

web/src/views/ProjectView.vue

@@ -344,7 +344,12 @@ async function onCreateInbox() {
         <p v-if="cards.loading && !cards.loaded" class="muted">Loading…</p>
 
         <div v-else class="kanban">
-          <section v-for="column in board" :key="column.key" class="kanban__col">
+          <section
+            v-for="column in board"
+            :key="column.key"
+            class="kanban__col"
+            :class="{ 'kanban__col--inbox': column.statusId === null }"
+          >
             <header class="kanban__head">
               <span class="kanban__title">{{ column.title }}</span>
               <span class="kanban__count">{{ column.cards.length }}</span>