v0.1.1 - field fixes from release night

Two fixes found by real usage within hours of v0.1.0 going public:

• arl serve now defaults to port 8765 (was: an ephemeral random port that left healthy dashboards running where no browser could find them). The port is documented in --help; if it's busy, serve fails closed with direction instead of silently picking another. --port 0 still gives an ephemeral port.
• arl report <run-id> works positionally alongside --run (conflicting ids and a missing id both fail closed with guidance).

599 tests passing. Install: uv tool install agent-run-ledger.