Fix 422 Unprocessable Entity when syncing to Mealie v3.12.0+

[TheZargs]

Description:
Syncing recipes to Mealie fails with 422 Unprocessable Entity for all recipes when using Mealie v3.12.0 or newer.
Environment:

kptncook: 0.0.29
Mealie: v3.12.0

Root cause:
In mealie.py, several HTTP requests use data= instead of json= or content= with the correct Content-Type header. Newer versions of Mealie are stricter about content type validation and reject requests without Content-Type: application/json.
The affected lines in src/kptncook/mealie.py:

# _post_recipe_trunk_and_get_slug (~line 270)
# WRONG:
r = self.post("/recipes", data=json.dumps(data))
# FIXED:
r = self.post("/recipes", json=data)

# _scrape_image_for_recipe (~line 280)
# WRONG:
r = self.post(scrape_image_path, data=json_image_url)
# FIXED:
r = self.post(scrape_image_path, content=json_image_url, headers={"Content-Type": "application/json"})

# _create_item (~line 312)
# WRONG:
r = self.post(f"/{endpoint_name}", data=item.json())
# FIXED:
r = self.post(f"/{endpoint_name}", content=item.json(), headers={"Content-Type": "application/json"})

# _update_recipe (~line 361)
# WRONG:
r = self.put(recipe_detail_path, data=recipe.json())
# FIXED:
r = self.put(recipe_detail_path, content=recipe.json(), headers={"Content-Type": "application/json"})