Function resolveValidationTargets

Resolve the Lighthouse target accounts pinned in a composable policy's ValidationPda for the given phase.

• If spec is not ProgramCall → [] (validation disabled).
• Fetches the ValidationPda derived from policyPda + phase + programId.
• If the account is missing/unreadable → [] (lets the on-chain pin-check reject loudly — matches scheduler/CLI behavior).
• Otherwise returns pinnedAccounts[0..numPinnedAccounts].

The ValidationPda itself is a named Anchor account and is not part of the returned slice (ADR-0016).