Add integration tests for execution persistence, metrics, and opportunity writing

- Implemented integration tests for the execution writer to ensure trade orders and PnL are persisted correctly.
- Created integration tests for the metrics calculator to summarize execution data accurately.
- Added integration tests for the opportunity writer to verify event persistence.
- Established PostgreSQL schema validation tests to ensure all expected tables, columns, and constraints exist.
- Removed outdated unit tests that relied on DuckDB and replaced them with tests using PgStore.

docs/DEPLOYMENT.md

@@ -7,16 +7,16 @@ This guide provides two supported deployment paths for Arbitrade on Coolify:
 
 Reference docs:
 
-- Coolify Applications: https://coolify.io/docs/applications
-- Coolify Build Packs: https://coolify.io/docs/applications/build-packs
-- Coolify Dockerfile Build Pack: https://coolify.io/docs/applications/build-packs/dockerfile
-- Coolify Nixpacks Build Pack: https://coolify.io/docs/applications/build-packs/nixpacks
-- Coolify CI/CD (Git providers): https://coolify.io/docs/applications/ci-cd
-- Coolify Gitea integration: https://coolify.io/docs/applications/ci-cd/gitea/integration
-- Coolify environment variables: https://coolify.io/docs/knowledge-base/environment-variables
-- Coolify persistent storage: https://coolify.io/docs/knowledge-base/persistent-storage
-- Coolify health checks: https://coolify.io/docs/knowledge-base/health-checks
-- Coolify Docker registry credentials: https://coolify.io/docs/knowledge-base/docker/registry
+- [Coolify Applications](https://coolify.io/docs/applications)
+- [Coolify Build Packs](https://coolify.io/docs/applications/build-packs)
+- [Coolify Dockerfile Build Pack](https://coolify.io/docs/applications/build-packs/dockerfile)
+- [Coolify Nixpacks Build Pack](https://coolify.io/docs/applications/build-packs/nixpacks)
+- [Coolify CI/CD (Git providers)](https://coolify.io/docs/applications/ci-cd)
+- [Coolify Gitea integration](https://coolify.io/docs/applications/ci-cd/gitea/integration)
+- [Coolify environment variables](https://coolify.io/docs/knowledge-base/environment-variables)
+- [Coolify persistent storage](https://coolify.io/docs/knowledge-base/persistent-storage)
+- [Coolify health checks](https://coolify.io/docs/knowledge-base/health-checks)
+- [Coolify Docker registry credentials](https://coolify.io/docs/knowledge-base/docker/registry)
 
 ## Common Runtime Configuration
 
@@ -32,14 +32,14 @@ Use these values in both deployment modes.
 
 - Add a persistent volume
 - Mount path: `/app/data`
-- Set DB path to: `DUCKDB_PATH=/app/data/arbitrade.duckdb`
+- Set PG connection: `PG_HOST=postgres`, `PG_PORT=5432`, `PG_DATABASE=arbitrade`, `PG_USER=arbitrade`, `PG_PASSWORD=arbitrade`
 
 ### Required environment variables
 
 - `APP_ENV=prod`
 - `APP_HOST=0.0.0.0`
 - `APP_PORT=9090`
-- `DUCKDB_PATH=/app/data/arbitrade.duckdb`
+- `PG_DATABASE=arbitrade`
 - `LOG_LEVEL=INFO`
 - `LOG_JSON=true`
 - `KRAKEN_API_KEY=<set-in-coolify-secret>`
@@ -135,7 +135,7 @@ Update flow for new releases:
 - Ensure the deployed image/wheel includes package templates under `arbitrade/web/templates/*`.
 - If you build from source, do not remove packaged template files under `src/arbitrade/web/templates`.
 - DB resets after deploy:
-- Confirm persistent mount exists at `/app/data` and `DUCKDB_PATH` points there.
+- Confirm PostgreSQL is reachable at `PG_HOST`.
 - Registry pull fails:
 - Re-check Docker registry credentials in Coolify.
 - App starts but unavailable externally: