#1788 chore: Keep Editor package sources under 500 lines

Summary

• Split 21 Editor god-class sources across PR-1…PR-7 into focused Extract Class / Move Method units so every Packages/src/Editor/**/*.cs file stays under 500 lines.
• Behavior-preserving refactors only: characterization tests where coverage was thin; Presentation windows keep delayCall / schedule patterns and Settings event wiring; no protocolVersion bump and no public API renames.
• Squash-merged child PRs into this integration branch: #1781 ExecuteDynamicCode, #1782 Screenshot, #1783 Input, #1784 Compile, #1785 Infrastructure, #1786 Domain migration rewrite, #1787 Settings/Wizard UI (manual smoke OK).

Test plan

• dist/darwin-arm64/uloop compile → 0 errors / 0 warnings on integration tip
• dotnet test tests/UnityCliLoop.CodeComplexity.Tests → 12 passed
• dist/darwin-arm64/uloop run-tests --test-mode EditMode full suite (running)
• find Packages/src/Editor -name '*.cs' | xargs wc -l → no file ≥500 (max ~489)
• CI all green including CodeRabbit
• Fable final review on the integration→v3-beta PR

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