Summary insert should preserve undo history

[krwg]

Summary

editor.setValue() breaks undo expectations.

Target milestone: 2.8.5
Work branch: 2.8.5/issue-7-summary-undo

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Problem

Full editor replace for summary apply.

Expected behavior

vault.modify preserves Obsidian undo stack where possible.

Suggested approach

Use vault.modify + view refresh; keep replace-latest separator logic.

Files / areas

• main.js
• services/summary.js

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Acceptance criteria

• Undo restores pre-summary body

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Metadata

Field	Value
Priority	P1
Milestone	2.8.5
Branch	2.8.5/issue-7-summary-undo