Add GitHub repo iteration example

[Octane0411]

Problem statement

The repository did not include a dedicated example showing how to run Symphony against a GitHub-hosted repository while using Linear as the tracker.

Scope summary

• add examples/github-repo-iteration/WORKFLOW.md
• add examples/github-repo-iteration/README.md
• document the required environment variables and launch command
• show a workflow configuration that enables repo cloning, networked CLI usage, PR creation, and Linear write-back

References

• SPEC.upstream.md
• prior demo validation against OasAIStudio/oas-demo

Validation

• git diff --check
• pnpm lint could not run in this worktree because node_modules is not installed and biome is unavailable