chore: [Remote rendering] Clean up renderer interface before adding a second mode

[LKasianAnsys]

Addresses #26

Until now, the renderer interfaces on both the server and the client had only ever had one real implementation. They've picked up code that only really belong to the vtk-wasm implmentation, and there's also some dead code that should be removed before building on it.

The server interface carried wasm-specific members, and each implementation kept its own copy of the camera and cross-section plane records. The browser interface had attachSceneGraph, which only had one live call that was no longer needed. Anything not needed here by a remote rendering implementation would need to be implemented as a no-op, so removing here now.

This PR:

• Removes unused members on both stacks
• Moves wasm-only members off the server interface onto the local renderer, which the local scene references directly
• Keeps the camera and cross-section plane records on the server-side renderer base instead of on the implementations
• Removes attachSceneGraph
• Moves full screen off the renderer, since it only touches the page, and renames the frontend's global edges method to match the renderer's.

Manual check:

• Load a scene with a multiblock dataset. Color a part by a variable; no errors on the server or console are logged.
• Click the wire frame widget: every part shows a wire frame. Clicking it again turns it off for every part.
• Toggle the bounding box on and off; it works as expected.
• Turn full screen on, then off; works as expected.
• Run save_state, change something in the scene, then load the file back in. The parts, camera and panels restore correctly.
• No browser console errors throughout