fix: prevent initial-load blocking in electron and web

[kaybarax]

Summary

• prevent startup from getting stuck behind an infinite loading state in both the Electron app and web app
• add a shell dev shim and startup flow updates so initial rendering can proceed without hard blockers
• include preview/startup script organization updates needed to support reliable local startup behavior

Test plan

• Start Electron app and verify first load completes without indefinite loader
• Start web app and verify first load completes without indefinite loader
• Verify shell renderer path initializes correctly in dev flow

Made with Cursor

[yiliush]

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[kaybarax]

I have read the Contributor License Agreement (CLA) and hereby sign the CLA.