fix(tasks): match /lists + /notes create pattern

Two concrete problems the user hit:
  1) /tasks overview had no visible "create" button — only an enter-to-submit
     input hidden behind a decorative Plus icon.
  2) /tasks/[id] add-task form had no visible submit button either.

Both now mirror the /lists + /notes pattern:

  /tasks — new "New list" button in the masthead (bg-slate-900 primary
    style matching "New list" on /lists and "New note" on /notes). Click
    creates an empty task_list and navigates to /tasks/[id] where the
    user names it inline via the new big editable title input
    (autosaves after NAME_SAVE_DEBOUNCE_MS, 500 ms — same hook as
    /lists/[id] and /notes/[id]).
  /tasks/[id] — sticky add-task footer gains a filled "+" submit button
    on the right; clicking it or pressing Enter both fire handleAdd.
    Input is now wrapped in the same rounded-lg card used on /lists/[id]
    so the two screens look identical.

i18n
  tasks_new_list = "New list" / "Nueva lista" (en / es).

Tests
  tasks.test.ts helper updated to drive the new button-then-title flow
  (same shape as lists.test.ts). T-UI-01..03 all pass.

just test-all → exit 0, 228 green, 2 skipped.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/messages/en.json

@@ -100,6 +100,7 @@
 	"list_finish_confirm_yes": "Yes, finish",
 	"list_finish_confirm_no": "Keep shopping",
 	"tasks_title": "Tasks",
+	"tasks_new_list": "New list",
 	"tasks_no_lists": "No task lists yet",
 	"tasks_create_first": "Create your first task list",
 	"tasks_new_list_placeholder": "New task list",

apps/web/messages/es.json

@@ -100,6 +100,7 @@
 	"list_finish_confirm_yes": "Sí, terminar",
 	"list_finish_confirm_no": "Seguir comprando",
 	"tasks_title": "Tareas",
+	"tasks_new_list": "Nueva lista",
 	"tasks_no_lists": "Sin listas de tareas",
 	"tasks_create_first": "Crea tu primera lista de tareas",
 	"tasks_new_list_placeholder": "Nueva lista de tareas",