refactor: remove engine v1 editor support

[kpal81xd]

Forum: https://forum.playcanvas.com/t/important-playcanvas-editor-support-for-engine-v1-ends-on-july-1st/42242

Changes

• Removes the Engine V1/Engine V2 switch UI and picker.
• Removes frontend engineV2/projectEngineV2 handling and trusts backend-provided engine version options.
• Removes legacy WebGL1 launch, migration, and warning paths from Editor and launch flows.

Manual smoke test

1. Open an older project previously configured for Engine V1; expected: the Editor opens without an Engine V1/V2 switch.
2. Open Settings > Engine and Publish/Download; expected: only backend-provided engine options are available.
3. Launch the scene; expected: WebGPU/WebGL2 launch options work and no WebGL1 option appears.

Checks

• I confirm I have read the contributing guidelines

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Project	Deployment	Actions	Updated (UTC)
editor	Ready	Preview, Comment	Jun 30, 2026 9:57am

[mvaligursky]

Just double checking. If user opens a project that has not been opened in years, we still handle V1 -> V2 migration for data, for example material properties?

[Maksims]

What will happen to our V1 projects on our accounts?

[mvaligursky]

What will happen to our V1 projects on our accounts?

See here: https://forum.playcanvas.com/t/important-playcanvas-editor-support-for-engine-v1-ends-on-july-1st/42242/6