feat(handlers): repair bad lockfile states when enforcement is disabled

What does this MR do?

Repairs inconsistent lockfile states caused by REGISTRY_FF_ENFORCE_LOCKFILES misuse. When the flag was disabled (default), lockfiles weren't managed at all, leaving many instances with incorrect states after metadata database migration.

Fixes:

• When filesystem-in-use lockfile exists but shouldn't (post-import)
• When filesystem-in-use lockfile is missing but should exist
• When both lockfiles are present, deletes the "extra" lockfile based on the configuration.

Context: The feature flag was incorrectly placed, causing early returns that prevented lockfile management entirely. This left migrated instances with filesystem-in-use still present and database-in-use missing—the opposite of intended state.

All of these fixes only happen when the feature flag is disabled, as that's the only time these lockfile mismanagement bugs can occur. If the user has enabled this feature flag already, they either have good lockfile states or have manually repaired them.

Related to #1776, !2647 (merged), !2648 (merged), !2649 (merged)

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