[Snapshots] PK snapshot: Override-aware preflight check

[kvch]

What to build

Make SnapshotKeyCheck respect strategy_overrides (skip ctid-forced tables) and primary_keys (treat as resolved).

Requirements

• ctid-overridden tables produce no finding
• Tables with a primary_keys entry produce no finding

Depends on

• [Snapshots] PK snapshot: schema preflight category + SnapshotKeyCheck #935 — schema preflight category + SnapshotKeyCheck
• [Snapshots] PK snapshot: Per-table primary_keys override #931 — Per-table primary_keys override
• [Snapshots] PK snapshot: strategy_overrides + mixed-schema export predicate #932 — strategy_overrides + mixed-schema export predicate