Automate patch upmerge from older release branches

[Copilot]

Description:

Patches to older release branches (e.g., release-1.5) weren't being propagated to newer releases and main. This workflow triggers on push to any release-* branch, compares versions via git tags, and creates PRs to upmerge if the current branch is older than latest.

Key implementation:

• Extracts version from branch name, finds latest via git tag --sort=-version:refname
• Numeric semantic version comparison (handles major/minor correctly)
• Branch existence check before PR creation to avoid failures
• Uses repo-sync/pull-request action for consistency with existing workflows

Security:

• Explicit token permissions: contents: read, pull-requests: write
• Uses PAT for branch protection bypass (same pattern as other workflows)

Related:
#141

Visual:
N/A - workflow automation only

TODO:

• Updated README documents
• Complete PR Body

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[devlinjunker]

will patches be in main already? or does this branching strategy expect that patches should be merged to an older release first (where issue is faced and the version is supported), and then propagated forward to future releases? @copilot

[Copilot]

will patches be in main already? or does this branching strategy expect that patches should be merged to an older release first (where issue is faced and the version is supported), and then propagated...

The branching strategy expects patches to be created on the older release branch first (where the issue is faced and the version is still supported), then propagated forward to newer releases and main.

This workflow triggers when a patch is pushed to an older release-* branch (e.g., release-1.5). It then creates PRs to upmerge those changes to:

1. The most recent release-* branch (e.g., release-1.7)
2. The main branch

This ensures that bug fixes in older supported versions are also applied to all newer versions, following the pattern described in issue #141.