ci: add GitHub Action to create Linear tickets from changelog

[factory-ben]

Automatically creates Linear tickets for new features when changelog files are updated and merged to main.

What it does

• Triggers on push to main when docs/changelog/*.mdx files change
• Parses the newest <Update> block for features under ## New features or ## Improvements
• Creates Linear tickets via GraphQL API with:
  • Title: [version] Feature Name
  • Description with changelog context
  • Due date 7 days from creation
  • Optional: assignee, project, and label

Required secrets

• LINEAR_API_KEY - Linear API key
• LINEAR_TEAM_ID - Team to create issues in

Optional secrets

• LINEAR_ASSIGNEE_ID - Auto-assign tickets
• LINEAR_PROJECT_ID - Add to a project
• LINEAR_LABEL_ID - Apply a label

[factory-droid]

Droid finished @factory-ben's task —— View job

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Code Review Complete ✅

Reviewed the new changelog-to-linear.yml workflow. Found 2 minor robustness concerns:

1. Line 92: JSON.parse could fail without helpful error context if Linear returns non-JSON responses (rate limiting, server errors)
2. Line 55: fs.readFileSync lacks existence validation for cleaner failure messages

Both are low-severity suggestions for improved error handling. Overall the workflow logic looks solid.