notion-md edit: conflict exits 0, not scriptable

[schickling-assistant]

Problem

notion-md edit swallows a body conflict to exit 0: editEditorPage catches NmdConflictError, relocates the draft to <page>.conflict.md, and returns a success EditResult{outcome:'conflict'}, so the editorExitCode teardown sees success → exit 0. A script cannot detect an edit conflict by exit code.

This is asymmetric with the exit-code contract (NmdConflictError → 7) and with the file-sync path, which does exit 7 on conflict.

Goal

notion-md edit conflict surfaces as a non-zero scriptable exit (7, matching the contract and the sync path), while still relocating the durable <page>.conflict.md and rendering the WARNING + fix: in the output.

Notes

Behavioral change to the engine's catch semantics (not the output seam) — deliberately out of scope for the #794 presentational output refactor, which preserves today's exit-0 behavior. Flagged during the Slice B milestone review.

Refs #794.

Posted on behalf of @schickling

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