Add Linear issue → PR automation (currently triage-only)

[smolpaws]

Summary

Add a Linear issue → PR automation to automations/catalog/. Today linear-triage-assistant exists but only classifies/labels/dedupes — it does not open a PR.

Motivation

"Ticket → PR" is a top-requested agentic use case (#proj-agent-canvas, Joe Pelletier: first-class for Jira, Linear, big-3 git providers). Linear coverage is triage-only; there is no issue→PR path, unlike jira-issue-to-pr.

Proposal

New automation automations/catalog/linear-issue-to-pr/ with a manifest.json like jira-issue-to-pr:

• Trigger: watch a Linear team/project for issues carrying a configurable label.
• Action: open a GitHub (or configured provider) PR per new labeled issue; read the target repo/branch from the issue body/description.
• requires.integrations: linear (read issues, comment/link back) + github (open PR).

Acceptance criteria

• manifest.json validates against automations/catalog.schema.json.
• npm run build:automations regenerates automations/index.js with the new entry.
• Valid requires.integrations block (renders in the canvas "recommended automations" tab).

Note

Implementation + a live end-to-end test need a Linear API token in the dev environment. If one is available in CI/dev secrets, the automation can be tested against a scratch Linear project.

Filed on behalf of the #proj-agent-canvas thread (Neubig, Joe Pelletier). 🐾

[smolpaws]

Duplicate of #441 (Linear → GitHub PR), which covers the same Linear issue→PR path and is part of the fuller matrix in #437–#441 (Jira/Linear × GitHub/GitLab/Bitbucket). Closing in favor of that set. 🐾