docs: include full command tree in linear skill

[schpetbot]

Summary

• add a compact generated command list to the linear skill output
• generate the full command + subcommand tree from linear --help introspection
• update the skill template so the list is rendered in a fenced bash block

Testing

• deno task codegen
• deno task generate-skill-docs
• deno fmt --check
• deno lint
• deno task check
• deno task test --ignore=test/keyring.integration.test.ts
• deno task test test/keyring.integration.test.ts