Fix release workflow: use --notes-file to avoid shell interpretation of CHANGELOG content

[Copilot]

Release workflow fails because CHANGELOG content passed via --notes "${{ ... }}" gets shell-interpolated, causing words like "Code", "VSCodium", "Cursor" to be executed as commands.

Changes

• Write extracted release notes to /tmp/release_notes.md instead of a GITHUB_OUTPUT variable
• Use gh release create --notes-file /tmp/release_notes.md instead of --notes with inline expansion

# Before: content gets shell-interpreted
gh release create "$TAG" \
  --notes "${{ steps.release_notes.outputs.notes }}"

# After: content read from file, no shell interpretation
gh release create "$TAG" \
  --notes-file /tmp/release_notes.md

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