Added the key commands, uppercase list headers, and dropped send

[siliconwitch]

The client half of the per-fleet key cycle (server PR: siliconwitchery/superstack-next#17), on the 0.0.3 version matching the server's gate.

Key commands

• key create <fleet_id> <label> prints the secret once with a keep-it-safe note; the label is mandatory.
• key list [fleet_id] shows key id, fleet id and name, the last five characters, and the label; --json for machines.
• key revoke <key_id> revokes without a prompt, matching member remove (a revoked key is replaceable, unlike a deleted fleet).

Headers

• Every list command now prints an aligned uppercase header row (ID FLEET FLEET NAME KEY LABEL, ID NAME ROLE, EMAIL ROLE), the docker/kubectl convention, so adjacent id columns read unambiguously. --json output and the empty-state messages are unchanged.

Send

• The send stub is gone per the design decision: posting data is the user's own HTTP client against the data endpoint with a fleet key, so the CLI never goes near it. The help section it lived in is now "Logs", holding tail.

Tests gained a stdout-capture helper, so list rendering and the printed secret are now asserted, and the mocks pin the exact paths requested. Verified with vet, the full suite, and an end-to-end smoke against a locally running server.