Document software factory setup through Agent Canvas UI

[neubig]

Desired Behavior

Provide a concise use-case tutorial for configuring a software factory from a fresh Agent Canvas installation through UI operations: model, saved GitHub credentials, scoped agent profiles, and four independent extensions automations (triage, developer, reviewer/QA, watchdog).

Acceptance Criteria

• Document the actual validated UI sequence and prerequisite capabilities/releases.
• Include selected screenshots from an end-to-end setup recording and retain the animated GIF.
• Explain per-role fine-grained PAT permissions and profile secret selection.
• Show how to target a repository, define independent tests, and observe issue-to-merge progress.
• Add the tutorial to the use cases navigation and validate links and docs checks.