feat: migrate receiptwitness to standalone repo with inlined common

Extract receiptwitness/ from the monorepo into cartsnitch/receiptwitness.
Inline the consumed modules from cartsnitch-common so there is no
cross-repo dependency.

- Add src/receiptwitness/shared/ with inlined models, schemas, constants, database
- Update all imports from cartsnitch_common to receiptwitness.shared
- Remove cartsnitch-common dependency from pyproject.toml
- Copy and update Alembic config (alembic.ini, alembic/)
- Update Dockerfile for standalone build context, add migration CMD
- Add CI workflow with lint, test, build, grype scan, deploy-dev, deploy-uat
- Add .grype.yaml

Co-Authored-By: Paperclip <noreply@paperclip.ing>

tests/test_pipeline/test_normalization.py

@@ -3,7 +3,7 @@
 import uuid
 from datetime import UTC, datetime
 
-from cartsnitch_common.models.product import NormalizedProduct
+from receiptwitness.shared.models import NormalizedProduct
 
 from receiptwitness.pipeline.normalization import (
     MatchMethod,