feat: add integration tests with docker-compose (#7)

[mikkeldamsgaard]

Closes #7

Changes

• 18 integration tests covering: wait-for (TCP/HTTP/timeout/multiple), render, fetch, exec, seed PostgreSQL/MySQL with cross-table refs, idempotency, reset, create database/schema, and 4 create-if-missing tests with known non-existing database names
• tests/docker-compose.yml — Postgres 16, MySQL 8.0, nginx services
• tests/fixtures/ — seed-postgres.yaml, seed-mysql.yaml, template.conf.tmpl
• .github/workflows/integration.yml — CI workflow with service containers
• Updated CHANGELOG.md and tests/README.md

How to verify

docker compose -f tests/docker-compose.yml up -d --wait
INTEGRATION=1 cargo test --test integration_test -- --test-threads=1
docker compose -f tests/docker-compose.yml down
cargo fmt --check
cargo clippy -- -D warnings
cargo test --all

All 29 tests pass (11 unit + 18 integration), clippy clean, fmt clean.

[Copilot]

Pull request overview

This PR adds comprehensive integration testing infrastructure using Docker Compose to test initium against real database services. It introduces 18 end-to-end tests covering all major commands (wait-for, render, fetch, exec, seed) with PostgreSQL 16, MySQL 8.0, and nginx services.

Changes:

• Added 18 integration tests for wait-for (TCP/HTTP/timeout/multiple targets), render, fetch, exec, and seed operations with PostgreSQL and MySQL
• Created Docker Compose configuration with Postgres 16, MySQL 8.0, and nginx services with health checks
• Added separate GitHub Actions workflow for integration tests using service containers
• Enhanced database interface to properly handle auto-increment ID columns in seed operations
• Updated documentation with integration test instructions and test scenario table

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/integration_test.rs	New integration test suite with 18 tests covering all major commands and database operations
tests/fixtures/template.conf.tmpl	Template fixture for testing render command with environment variable substitution
tests/fixtures/seed-postgres.yaml	PostgreSQL seed specification with cross-table references for testing seed functionality
tests/fixtures/seed-mysql.yaml	MySQL seed specification with cross-table references for testing seed functionality
tests/docker-compose.yml	Service definitions for Postgres, MySQL, and nginx with health checks on non-standard ports
tests/README.md	Documentation for running unit and integration tests with scenario descriptions
src/seed/executor.rs	Passes auto_id column name to database layer for proper ID retrieval
src/seed/db.rs	Enhanced insert_row to accept auto_id_column parameter for RETURNING clause in PostgreSQL
CHANGELOG.md	Documented new integration testing infrastructure and test coverage
.github/workflows/integration.yml	CI workflow for integration tests with service containers

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