Discovery: add schema policy for duplicate and hierarchy evaluation

[BadgerOps]

Follow-up to #187 and PR #188.

Summary

Introduce configurable schema policy for duplicate detection and hierarchy validation across accounts, regions, pools, and custom layouts.

Why

PR #188 uses conservative built-in conflict detection. CloudPAM should support different operator models such as pool per account, pool per region, global pool with account children, and custom hierarchies.

Scope

• Add an internal schema policy object with conservative defaults.
• Support account-level, region-level, global, and custom/manual ownership strategies.
• Use policy when evaluating duplicate CIDRs, overlaps, and parent placement.
• Surface policy assumptions in conflict evidence.

Acceptance Criteria

• Duplicate detection behavior can vary by selected policy.
• Tests cover account-level, region-level, global, and custom policy examples.
• Conflict evidence explains which policy caused a duplicate or nesting issue.