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>

README.md

@@ -0,0 +1,29 @@
+# ReceiptWitness
+
+Purchase data ingestion service for CartSnitch. Authenticates with grocery retailer web portals (Meijer, Kroger, Target) via Playwright, scrapes purchase history, and writes structured records to the shared PostgreSQL database.
+
+## Quick Start
+
+```bash
+# Install dependencies
+pip install -e ".[dev]"
+
+# Run tests
+pytest tests/ -v
+
+# Local dev with Docker Compose
+docker-compose up
+```
+
+## Architecture
+
+- **Scrapers:** Playwright-based browser automation for each retailer
+- **Parsers:** Converts raw receipt data to structured `Purchase` / `PurchaseItem` records
+- **Database:** SQLAlchemy 2.0 async; models inlined under `src/receiptwitness/shared/`
+- **Events:** Publishes `cartsnitch.receipts.ingested` to Redis after ingestion
+
+## Branches
+
+- `dev` — development, auto-deploys to dev cluster
+- `uat` — user acceptance testing
+- `main` — production, auto-deploys to prod cluster