Add GitHub mode to MyCoder for working with issues and PRs

[bhouston]

Implements GitHub mode for MyCoder that enables the agent to work with GitHub issues and PRs as its primary workflow.

When enabled, the agent will:

• Start from existing GitHub issues or create new ones for tasks
• Create branches for issues it's working on
• Make commits with descriptive messages
• Create PRs when work is complete
• Create additional GitHub issues for follow-up tasks or ideas

Changes include:

• Added GitHub mode detection in the system prompt
• Updated documentation in README.md and CLI README.md
• Added dedicated documentation in docs/github-mode.md
• Created a changeset for version tracking

Closes #67

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ Error: 400 deepseek-reasoner does not support Function Calling Object.doGenerate(config.ts) View Issue

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[github-actions]

🎉 This PR is included in version mycoder-agent-v1.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[github-actions]

🎉 This PR is included in version mycoder-v1.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀