All tasks tab: match the new-card form layout used everywhere else

Was the stacked .form pattern (visible "New card" label above a
full-width input). Now .kanban__new, same as the kanban columns and
sidebar inbox: compact field + placeholder/aria-label in place of the
visible label, on one line with the icon button. Kept form--new-card
for the border-top separator above it.

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

web/src/views/ProjectView.vue

@@ -206,11 +206,16 @@ async function onCreateInColumn(column: Column) {
           />
         </ul>
 
-        <form class="form form--new-card" @submit.prevent="onCreate">
-          <label>
-            <span>New card</span>
-            <input v-model="newText" class="field" type="text" maxlength="1000" required />
-          </label>
+        <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"