fix(#683): claw skills remove/add/uninstall/delete emits typed error, exit 1

[code-yeongyu]

Summary

Fixes #683: claw skills remove/add/uninstall/delete no longer silently exits 0 with help text (stealth-success). Instead, it emits a typed kind:"unsupported_skills_action" structured error and exits 1.

Changes

• Guard in parse_args: Before dispatching skills commands, check if the first word is remove, add, uninstall, or delete. If so, return a structured error string containing "unsupported skills action".
• Error classification: Added unsupported_skills_action to classify_error_kind() so JSON output surfaces the correct machine-readable kind.
• Regression test: Added unsupported_skills_actions_return_typed_error_683 which verifies all four forbidden actions error out and are classified correctly.
• Build fixes: Fixed pre-existing compile errors (stale retry_after field in ApiError, missing Team variant in SlashCommand) so the crate builds.

Verification

cd rust && cargo test -p rusty-claude-cli --bin claw unsupported_skills_actions_return_typed_error_683

Test plan

1. claw skills remove → exits 1, stderr contains "unsupported skills action: remove", JSON output has kind: "unsupported_skills_action"
2. claw skills add → same pattern
3. claw skills uninstall → same pattern
4. claw skills delete → same pattern
5. claw skills list / claw skills install ./path / claw skills help → continue to work normally