Walks every string-valued manifest field after load and rejects values
containing `{{...}}` (conservative: requires both `{{` and `}}`). Catches
wizard bugs that would emit literal `{{MEMORY_PROJECT}}` into the
generated agent .md. Four unit tests cover role/memory_project/single-brace
accept/empty-accept cases.
root.parent().unwrap() at main.rs:45 panicked if AGENT_ROOT pointed at a
filesystem root (e.g. AGENT_ROOT=/). Now falls back to root itself via
.unwrap_or(root.as_path()) so the 'OK <manifest> → <path>' line just
prints the absolute path in that edge case instead of aborting.
