--control took the next argument as its port and dropped it when it wasn't a number, so the app
started without a control server and `--control --automation-read-root DIR` opened DIR as a
document. automation_args::ControlArg now reads --control <port> or --control=<port> once and
requires a port from 1 to 65535; VECTORCRAFT_CONTROL_PORT must be one too, checked only when
--control isn't given so --control and --version win over a bad value. Errors go through the
same exit as the root flags (#1157).
Tests: unit tests in automation_args.rs; tests/automation_args.rs runs the binary for each bad
form and checks the exact message and a prompt failing exit.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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