docs(agents): add repository guidance

[lefoulkrod]

What changed

• Adds a minimal root agent guide with the canonical source gate.
• Records the engine/platform boundary for Podman operations.
• Points lifecycle and TUI work to the disposable VM lab suites.

How it was tested

• make verify in golang:1.25-bookworm
• git diff --check
• Confirmed the referenced VM test targets and documentation exist.

Release note

None: Adds development-agent guidance only; CLI behavior is unchanged.

Release and security check

• I considered whether this changes permissions, downloaded software, executed commands, dependencies, configuration files, or release artifacts.
• No dependencies were added or updated.
• User-facing documentation and tests were updated where needed.