Server actions + optimistic UI for the notes form

[ThomasHartDev]

adds a /data-patterns route that mutates a note list through a server action, so there's no client fetch handler at all. the new note shows immediately with useOptimistic and reverts on its own when the write fails, with useActionState holding the confirmed list plus the last error and useFormStatus driving the pending button. pulled the mutation logic into a plain applyAdd function with an injected store so validation, the fail path, and the store-throws path are all tested without the next runtime. theres a checkbox to force a failure so you can watch the optimistic note disappear and the error render. tests cover the reducer folding, trimming/length validation and confirmed state staying put on every failure mode.