Remove obsolete GUI loop facade

[thenderson21]

Summary

• remove the unused pre-release guiRun/guiLoop facade
• eliminate unresolved appRender/appUpdate references from the public AiVectra library
• keep application event-loop ownership in application modules

Validation

• ./scripts/test-all.sh
• git diff --check

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Update the runtime contract when removing guiRun

Any app authored against the repository's current contract now fails to resolve guiRun: test-fixtures/HelloWorld/AGENTS.md:6 explicitly requires guiBuild and guiRun, while SPEC/APP_RUNTIME.md:5-18 and SPEC/APP_RUNTIME.md:112-121 still state that AiVectra supplies the GUI adapter and samples consume its public runtime API. Because this hunk removes the only definition and export without updating those contracts or providing the promised application-owned replacement, canonical consumers have no implementable lifecycle; update the SPEC and fixture guidance/sample to the new path in the same change.

AGENTS.md reference: AGENTS.md:L114-L119

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