feat: reactive dependency-conflict primitives for targeted matview drops

[Th3Mouk]

Why

When a schema migration tries to DROP TABLE / DROP COLUMN or ALTER COLUMN … TYPE on a relation a managed materialized view reads, PostgreSQL blocks the DDL. The bundle's deploy lane currently clears this by dropping every managed materialized view up-front. This PR adds the framework-agnostic primitives needed to instead drop only the conflicting closure (a future reactive_retry lane strategy in the bundle, gated on th3mouk/materialized-view ^1.2).

Primitives only — no existing behaviour changes.

What

• Core\Sql\DependencyConflictSqlState — recognises the two blocking SQLSTATEs by walking the DBAL driver-exception chain, never the (locale-dependent) message text:
  • 2BP01 dependent_objects_still_exist — blocked DROP TABLE / DROP COLUMN
  • 0A000 feature_not_supported — blocked ALTER COLUMN … TYPE
• Core\Dependency\PostgresDependencyConflict — best-effort, locale-aware parse of the blocked relation + named dependents (the DETAIL list is only a seed; PostgreSQL caps it at 100 entries). Core\Sql\QualifiedName adds the quote-aware identifier scanner.
• Core\Dependency\CatalogDependencyResolver::resolveConflictClosure() — resolves the authoritative closure from the catalog: seeds via to_regclass, walks pg_depend/pg_rewrite by OID from an arbitrary relation (a plain table is not a node in the managed graph), classifies each dependent managed/unmanaged, orders dependents-first. Reuses DependencyGraph for ordering.
• Core\MaterializedViewManager::dropConflictClosure() — drops the managed closure in order, refusing (UnmanagedDependentFound) when any unmanaged dependent is present unless DropDependentPolicy::Cascade. The drop set is always confirmed against the catalog, never the error text alone.
• Core\Sql\ManagementMarker — isManagedComment() / readHash() read-side helpers (top-level marker-key check, not a substring match).

Tests

• Unit: SQLSTATE gate (chain-walk, message-decoy negatives), parser fixtures (2BP01 drop-table/drop-column incl. a column named like the of table marker, schema-qualified double-quoted names, 0A000 rule, truncation, non-English → not parsed), QualifiedName::scan/render, marker read helpers, closure VO merge.
• PG integration (PG 14–17): real 2BP01 DROP COLUMN and 0A000 ALTER TYPE provoked against a live server → parsed, surgically cleared, blocked DDL then succeeds; managed drop-ordering from the blocked table; guard refusal when an unmanaged view is in the closure.

Gates green locally: cs:check, stan (level 8, no baseline), test:unit (590), test:pg (11).