Redesign CLI flags, help, and argument validation

[madeye]

The five C CLI programs now expose descriptive, role-specific long flags such as --server-port, --listen-port, and --destination, while retaining working short aliases. Help is grouped by purpose and includes --version.

Explicit transport and address-family flags override configuration, with the last flag winning: for example, --tcp-only --ipv4-first overrides a UDP-only, IPv6-first configuration. Invalid options, missing arguments, invalid numeric values, and positional arguments return status 2 with diagnostics on stderr that omit argument values. Previously ignored server/manager -l is now rejected. Doxygen HTML and man-page sources document the new interface and compatibility details.

Validation on macOS after rebasing onto current master:

• Build and all 36 CTest tests, including CLI subprocess and live configuration-override tests.
• 131 ss-setup assertions and 10 MB relay stress tests across three ciphers.
• actionlint, pinned Ruff checks, and whitespace checks.
• 10 documentation regression tests, Doxygen HTML/man builds, and source/rendered documentation consistency checks.