ci: add label-driven backport workflow

[harshtandiya]

What

Adds .github/workflows/backport.yml, a label-driven GitHub Action (korthout/backport-action) that automates cherry-picking a merged PR onto a maintenance branch.

Why

We just cut 1.0.0. With develop as the forward line and main as the stable v1 line, any v1 fix now has to land in two places. Doing that by hand is easy to forget, so fixes silently miss the release line. This makes the backport one label away.

How it works

1. Add a backport main label to a PR against develop.
2. On merge, the action cherry-picks the (squashed) commit onto main and opens a [Backport main] … PR linking back to the original. Normal CI runs on it.
3. On conflict it does not open a PR — it comments the manual git steps on the original PR so nothing is silently dropped.

The label_pattern: '^backport ([^ ]+)$' scales to future lines (backport <branch>) without editing the workflow.

Follow-ups (not in this PR)

• Create the labels: backport main (and optionally backport-failed, no-backport).
• Standardize develop on squash-merge so each backport is one clean cherry-pick.
• Optional: add develop to the push trigger in ci.yml so the dev line is tested on merge too.

🤖 Generated with Claude Code

https://claude.ai/code/session_013PntNpMSKA2tkugCR3rupb

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Generated by Claude Code

[greptile-apps]

Greptile Summary

This PR adds automated, label-driven backports for merged pull requests. The main changes are:

• A workflow for creating backport pull requests against maintenance branches.
• Support for triggering backports during merge or by adding a label later.
• Conflict guidance and label copying for generated pull requests.
• An immutable pin for the write-capable third-party action.
• Filtering that prevents backport labels from propagating to generated pull requests.

Confidence Score: 5/5

This looks safe to merge.

• The action now uses an immutable commit pin.
• Generated pull requests no longer inherit labels that would trigger another backport.
• No blocking issue was confirmed in the updated workflow.

Important Files Changed

Filename	Overview
.github/workflows/backport.yml	Adds the backport workflow, pins its external action, and excludes backport-control labels from generated pull requests.

_{Reviews (2): Last reviewed commit: "ci: harden backport workflow" | Re-trigger Greptile}