fix(ci): simplify dev release install instructions to use install.sh

[drew]

Summary

Replace the verbose, gh-CLI-dependent install instructions in the dev release notes with a single curl | sh one-liner using the published install.sh script. This also removes the per-platform asset table since the install script handles platform detection automatically.

Related Issue

Follows up on #416 which published the install script in release workflows.

Changes

• Replaced multi-line gh release download shell snippet with curl | OPENSHELL_VERSION=devel sh one-liner
• Removed the per-platform assets table (the install script handles this)
• Changed "automatically built" to "automatically published" for clarity

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)