Resolve pending render entities by main entity

[stuartparmenter]

Objective

Fix meshes losing pending specialization when their render entity changes while they remain visible, such as when adding a component that requires SyncToRenderWorld.

Solution

Resolve pending entries by main entity in both specialization and queueing, using the current visible render entity. This also skips pending entities that are no longer visible and preserves queue deduplication.

Testing

Checked the iterator logic in an isolated Rust harness: stale render IDs and invisible pending entries fail before the fix and pass afterward. Queue deduplication and GPU-visible retries still pass. Formatting checks passed.

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This was AI assisted w/ Fable when tracking down a bug in my game. Looked at storing only main entities in the pending queues, but that would be a larger refactor, so went with the focused fix.