Replace utils/jay_diff.py with jaydiff package from jayfield/jaypy

Remove the local copy of jay_diff and its tests/data; switch all four
import sites to `jaydiff.diff.diff_full` / `jaydiff.merge.merge_full`
from the shared Gitea package (http://192.168.22.90:3001/jayfield/jaypy).
Add the package as a VCS dependency in requirements.txt.

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

collect.py

@@ -56,7 +56,7 @@ from server import log_config, network, we_connect
 from carconnectivity.errors import AuthenticationError, TemporaryAuthenticationError
 from server.data_model import ALL_DOMAINS, collect_snapshot, apply_procedural
 from server.storage_helpers import auto_out_path, load_last_24h_records, load_store, save_store
-from utils.jay_diff import jay_diff_full
+from jaydiff.diff import diff_full as jay_diff_full
 
 log = logging.getLogger(__name__)