Add multi-window editor support

[boomzero]

Summary

• add independent editor windows with canonical document ownership and duplicate-file focusing
• reuse untouched bootstrap windows while opening New/Open actions in separate windows when needed
• scope presentation/debug windows and IPC access to their owning editor
• add cross-platform single-instance file routing, safe Save As reservations, and sequential multi-window quit handling
• document the architecture and add multi-window lifecycle tests

Validation

• npm test — 143 tests passed
• npm run typecheck — passed
• npm run lint — passed
• npm run build — passed

[chatgpt-codex-connector]

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[boomzero]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 21557ff8ec

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[boomzero]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 7fd994b5c5

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".