fix: enforce write phase completion gate and wire done endpoint

- GET /write now checks all groups are written/skipped before showing
  the completion screen; incomplete sessions are redirected to the first
  draft group
- POST /write/done now accepts form data (not JSON) and redirects to
  /export; wired up from the completion screen via a <form> POST button
- phase5.html extra_scripts block wrapped in {% if group %} to prevent
  Jinja errors when group is None on the completion screen

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

services/travel-memories/app/routes/write.py

@@ -13,6 +13,11 @@ def write():
     total = len(active_groups)
     group = active_groups[group_idx] if group_idx < total else None
     done_count = sum(1 for g in active_groups if g.status in ("written", "skipped"))
+    if group is None:
+        all_done = all(g.status in ("written", "skipped", "exported") for g in active_groups)
+        if not all_done:
+            first_incomplete = next(i for i, g in enumerate(active_groups) if g.status == "draft")
+            return redirect(url_for("write.write", album_id=album_id, group_idx=first_incomplete))
     photos = []
     if group:
         by_id = {p.id: p for p in state.photos}
@@ -86,12 +91,13 @@ def skip():
 
 
 @bp.post("/write/done")
-def done():
-    body = request.get_json()
-    album_id = body["album_id"]
+def write_done():
+    album_id = request.form["album_id"]
     state = load_state(album_id, current_app)
+    if state is None:
+        return jsonify({"ok": False, "error": "not found"}), 404
     if "write" not in state.phases_completed:
         state.phases_completed.append("write")
     state.phase = "export"
     save_state(state, current_app)
-    return jsonify({"ok": True, "redirect": f"/export?album_id={album_id}"})
+    return redirect(f"/export?album_id={album_id}")