Good first issue: add three real-world Recursive Canopy examples

## Goal

Help new users understand when CodeCanopy should create a nested tree and when Ponytail should collapse the work to one agent.

Add three concise, repository-neutral examples:

1. A frontend and backend feature with one shared contract.
2. A bug fix that stays atomic after tracing the shared root cause.
3. A security-sensitive change with an independent reviewer and explicit authority boundary.

## Each example must show

- The user requirement.
- The ownership tree.
- The artifact dependencies.
- Owned or read-only paths.
- Acceptance checks.
- The bottom-up integration order.
- Why any tempting extra node was collapsed.

## Acceptance

- Examples use no customer data or private repository details.
- No example claims runtime behavior that CodeCanopy does not provide.
- At least one example reaches depth two or greater.
- At least one example remains a single node.
- Markdown links and formatting pass the repository checks.

Comment with the example you want to own before opening a pull request.