Combine server host and port with strict IPv6 endpoint parsing

[madeye]

Clients now accept --server example.com:8388 and --server '[2001:db8::1]:8388' without a separate server-port flag. Repeated endpoints retain their individual ports; legacy -s HOST -p PORT and configured fallback ports remain supported.

The CLI parser validates brackets, IPv6 literals and scope IDs, and ports from 1 to 65535. Bare IPv6 is always treated as a host, never split at its last colon. Embedded ports override fallback ports regardless of option order. SIP003 rejects endpoints with conflicting ports because its interface exposes a single remote port.

Updated help, Doxygen documentation, parser/CLI regression tests, and the relay stress test to use combined endpoints.

Validation:

• Local build, 36 CTest tests, 131 ss-setup assertions, actionlint, pinned Ruff, and whitespace checks.
• Three-cipher relay stress tests with 10 MB transfers using combined endpoints; IPv6 loopback relay also verified.
• Ten documentation regression tests, Doxygen HTML/man builds, and rendered/source consistency checks.