Add phase 4: AI cleanup and photo/text import via OpenAI

- recipes/ai.py: Chat Completions with strict JSON schema (Structured
  Outputs), Pydantic re-validation, plausibility clamping, prompt treats
  input as data only
- "Mit KI aufbereiten" on create/edit form returns an editable draft
- Import page: photo/screenshot (vision, downscaled JPEG, not stored) and
  pasted text; drafts pre-fill the recipe form with a preview
- Clear UI messages for timeout, rate limit, quota, auth, model and
  connection errors; without OPENAI_API_KEY AI features show a notice
- Optional per-user and global daily AI limits (default unlimited)
- Tests for response parsing, schema strictness, error mapping, views

Co-Authored-By: Claude Opus 5.5 <[email protected]>

static/js/app.js

@@ -39,3 +39,25 @@ document.addEventListener("change", (event) => {
   });
   acquire();
 })();
+
+// Long-running submits (AI): show progress on the clicked button and prevent double submits.
+// Disabling happens after the browser has captured the form data (incl. the clicked button).
+document.addEventListener("submit", (event) => {
+  const button = event.submitter;
+  if (!button || !button.dataset.busyText) return;
+  setTimeout(() => {
+    event.target.querySelectorAll("button[type=submit]").forEach((b) => {
+      b.dataset.label = b.dataset.label || b.textContent;
+      b.disabled = true;
+    });
+    button.textContent = button.dataset.busyText;
+  }, 0);
+});
+
+// Back/forward cache: restore buttons disabled by the handler above.
+window.addEventListener("pageshow", () => {
+  document.querySelectorAll("button[data-label]").forEach((b) => {
+    b.disabled = false;
+    b.textContent = b.dataset.label;
+  });
+});