feat: make Doctrine DBAL optional via a Connection port (DBAL + PDO adapters)

[Th3Mouk]

Why

The core engine only needs to run statements, fetch rows and open a transaction — a tiny surface. Expressing that as a port frees Core from any database library, so a project without Doctrine can drive PostgreSQL materialized views over a bare PDO connection, while Doctrine stays the recommended, natively-supported backend.

What

• Core\Database port — Connection (5 methods), ParameterType (enum), DatabaseException (carries the SQLSTATE, so 42P01/3F000 missing-dependency handling stays backend-agnostic). The whole synchronous engine runs on this; Core no longer depends on Doctrine.
• Two adapters
  • Dbal\DbalConnection — wraps a Doctrine DBAL connection; keeps primary/replica routing, middlewares and profiling; maps DBAL\Exception → DatabaseException.
  • Pdo\PdoConnection — wraps a bare PDO handle (pdo_pgsql); no extra Composer dependency.
• Manager factories — new forDriver(Connection) and forPdo(\PDO); forConnection(DBAL\Connection) is unchanged and now wraps the connection in DbalConnection internally.
• IdentifierQuoter is PostgreSQL-native (no DBAL platform), byte-identical output.
• composer.json — doctrine/dbal moves require → require-dev + suggest; the core requires only php and psr/log. ext-pdo_pgsql is suggested for the PDO path.

Backward compatibility

Fully BC. forConnection(), MaterializedViewMigrationSql, RefreshTargetResolver (still returns a DBAL Connection) and AsyncRefreshRequest are unchanged, so existing Doctrine code and the Symfony bundle need no changes. The DBAL type names that remain in Core (the forConnection convenience and the async-refresh resolver contract) are never loaded on the PDO path.

Validation

All CI gates green, plus the new PDO adapter exercised against a real PostgreSQL:

Gate	Result
cs:check	0 issues
stan	No errors
test:unit	552 tests
test:pg	12 tests (incl. PdoConnectionTest against a live PostgreSQL)

New tests: tests/Unit/Dbal/DbalConnectionTest (delegation, ParameterType mapping, exception→SQLSTATE, primary/replica routing) and tests/Integration/Pdo/PdoConnectionTest (queries, typed params, transactional commit/rollback, SQLSTATE).

Docs

README, getting-started, architecture, design-rationale (decision #1 reframed), a refresh/locking note, a new docs/guide/connection-backends.md, and CHANGELOG [1.2.0].