docs: --help documents the CLI for agents

[alukach]

Stacked on #47.

Agents learn a CLI from --help, which always matches the installed version, so this makes it complete enough to use on its own.

• No blank help: --title and --description on product create/edit now have help lines. A new test, every_command_and_argument_has_help, fails on any command or argument without one.
• Agent summary: source-coop --help ends with a "For scripts and agents" block (FOR_SCRIPTS in src/main.rs) covering --json and the error shape, running without prompts (SOURCE_PROMPT_DISABLED, -F -, --yes), SOURCE_TOKEN, and exit codes. -h stays short.
• Examples in each product subcommand's help.
• AGENTS.md gets a short "Help is the agents' documentation" section: help is the reference, the README is the guide, and a skill or llms.txt should point to --help rather than copy flags.
• README.md notes that --help carries this summary.

Checked with cargo fmt --check, cargo clippy --all-targets -- -D warnings, cargo test and cargo test --features staging.

🤖 Generated with Claude Code

[claude]

Claude finished @alukach's task in 11s —— View job

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✅ No blocking issues — safe to merge.

I read the diff and checked that SOURCE_TOKEN and SOURCE_PROMPT_DISABLED exist and behave as FOR_SCRIPTS says. I did not run the build or tests.

• The new help text matches the code and the README.
• every_command_and_argument_has_help, help_examples_parse and help_headings_are_styled_like_clap_s cover the help rules in AGENTS.md.
• shlex is a dev-dependency only, so it doesn't reach the release binary.

Simplify (ponytail)

• Cargo.toml:52 — shlex is a new dev-dependency used only for splitting example lines. It could be dropped by splitting on whitespace, since the examples quote only "My data" and '{"title": "My data"}'. That breaks as soon as an example needs richer quoting, so keeping it is fine.

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💰 Estimated review cost: $0.11 · 0m10s · 5 turns