Discovery: define and enforce stale resource import rules

[BadgerOps]

Follow-up to #187 and PR #188.

Summary

Decide and enforce whether stale discovered resources can be imported, linked, or resolved.

Why

Issue #187 calls out validating that an object is still present in latest discovery or that stale data is explicitly acknowledged. PR #188 does not yet add a specific stale import policy.

Scope

• Define policy for importing stale resources: block, warn with acknowledgement, or allow for selected actions.
• Add API validation in preview/apply.
• Show stale status and required acknowledgement in the UI.
• Include stale state in conflict/import evidence.

Acceptance Criteria

• Stale discovered resources cannot be silently imported.
• Preview explains the stale-resource decision clearly.
• Apply enforces the same policy as preview.
• Tests cover stale resource preview and apply behavior.