fix: Task back button navigates to correct recipe (not version_id)

- Add recipe_id property to RecipeTask model (via version relationship)
- Add recipe_id to TaskResponse schema
- Eager-load version in _get_task_or_404 query
- Use task.recipe_id instead of task.version_id in task_execute template URLs

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

server/models/task.py

@@ -39,6 +39,13 @@ class RecipeTask(Base):
         {"mysql_engine": "InnoDB", "mysql_charset": "utf8mb4"},
     )
 
+    @property
+    def recipe_id(self) -> int | None:
+        """Shortcut: recipe_id via the version relationship."""
+        if self.version:
+            return self.version.recipe_id
+        return None
+
     def __repr__(self) -> str:
         return f"<RecipeTask #{self.order_index} '{self.title}'>"