feat: structured database connection config (#39)

[mikkeldamsgaard]

Summary

• Add discrete connection fields (host, port, user, password, name, options) to DatabaseConfig as an alternative to url/url_env
• Build connections using driver-native APIs (PostgreSQL key-value DSN, MySQL OptsBuilder), bypassing URL parsing entirely — passwords with @, %, : etc. work without encoding
• Validate mutual exclusivity: structured fields and url/url_env cannot be combined

Closes #39

Test plan

• 168 unit tests pass (6 new: schema parsing, DSN building, connection resolution, escaping)
• 20 integration tests pass against real PostgreSQL 16 and MySQL 8.0 (2 new: test_seed_postgres_structured_config, test_seed_mysql_structured_config)
• cargo clippy -- -D warnings clean
• cargo fmt -- --check clean

cargo test
cargo clippy -- -D warnings
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

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR adds structured database connection configuration as an alternative to URL-based connection strings, closing issue #39. Users can now specify host, port, user, password, name, and options fields directly, avoiding URL-encoding issues with special characters in passwords. Connections are built using driver-native APIs (PostgreSQL key-value DSN, MySQL OptsBuilder).

Changes:

• New discrete connection fields on DatabaseConfig with mutual exclusivity validation against url/url_env
• Driver-specific structured connection logic: PostgreSQL key-value DSN builder and MySQL OptsBuilder integration, with SQLite explicitly rejected
• Comprehensive tests (unit + integration), documentation, and an example spec file

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/seed/schema.rs	Adds structured fields to DatabaseConfig, validation, and has_structured_config() helper; moves URL resolution out of SeedPlan
src/seed/db.rs	Refactors connect() to accept DatabaseConfig, adds connect_structured(), build_postgres_dsn(), escape_dsn_value(), and unsupported_driver_error()
src/seed/mod.rs	Updates call site to pass &plan.database instead of a resolved URL string
docs/seeding.md	Documents both connection styles, field reference table, and resolution order
examples/seed/structured-config-seed.yaml	Example spec using structured config with templated password
tests/input/seed-postgres-structured.yaml	Integration test fixture for PostgreSQL structured config
tests/input/seed-mysql-structured.yaml	Integration test fixture for MySQL structured config
tests/integration_test.rs	Two new integration tests verifying structured config with real databases
CHANGELOG.md	Documents the new feature

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