Mirror remote components into the inspector's remote world

[jbuehler23]

Stacked on #26014. Review the last commit only.

Objective

Part of #23013.

#26014 mirrors remote entities into a separate world but only inserts their names and parents, so selecting a remote entity shows almost nothing. This fills the remote world with real component values so the details panel works the same for a remote app as for the local one.

Solution

Following Zeophlite's idea of treating the remote app as just another world, every component the polls already receive is now inserted into the remote world, as long as inserting it can't do anything besides store the value.

• the full poll and a fetch of the selected entity both write into the world, values are deserialized off the main thread and only written when they change
• components that vanish remotely are removed
• only components without hooks are inserted, since a hook could spawn an entity that takes the index of a later remote entity, or depend on state the remote world doesn't have. Hooks aren't public on ComponentHooks, so each type is probed once on a separate empty world, checking its required components too. ChildOf is the one exception, its hook only builds Children
• relationship targets like Children are never inserted from JSON, since that detaches every child, they're built from ChildOf instead
• components with hooks, like PointerId and PointLight, show their raw JSON read-only in the details panel instead
• each entity records what came from the remote app, so required components that only got added locally stay hidden, components the remote app couldn't serialize get a note, and unregistered types show as raw JSON

Some bevy_ecs changes would make this simpler or more complete. A public accessor on ComponentHooks would replace the probe. A data-only insert that skips hooks and observers, or entity ranges, would let components with hooks be inserted too. And the reserve and set-generation API mentioned in #26014 would replace the allocator workaround.

A follow-up could also replace the raw JSON fallback with typed fields, by fetching the server's type schema (registry.schema) and building dynamic reflected values from it, so types the inspector doesn't know or that have hooks still get proper widgets.

AI disclosure

This builds on Zeophlite's world design from #26014. Before writing any code I had AI research what breaks when you insert arbitrary components into a bare world, which turned up the generation, allocator, PointerId and Children problems, then implement it with a test for each and check it end to end against the server example. I reviewed the design and the changes.

[eugineerd]

I haven't read through everything properly so I'm not sure if it's an issue, but something I encountered when experimenting with remote world concept is that if you insert just RelationshipSources you lose ordering present in RelationshipTargets.

[jbuehler23]

Good catch! The mirror now keeps the server's Children order and sorts the mirrored Children to match after each poll, without running any hooks. It's just Children for now since there's no generic way to reorder other relationship targets