Reject unknown seconv MCP server options

[Blackspirits]

Summary

The seconv README states a global CLI contract: an unrecognised option is an error, never a silent no-op.

Upstream PR SubtitleEdit#14129's McpServerHost.RunAsync only checks whether --verbose / -v is present and silently ignores every other argument. A typo such as seconv mcp --verbse therefore starts the server normally instead of failing, unlike the rest of seconv.

This change:

• accepts only --verbose and -v after the mcp subcommand;
• reports the first unknown option to stderr and returns exit code 1 before starting the protocol server;
• adds a process-level regression test that runs seconv.dll mcp --verbse and verifies the failure contract.

Validation

• based exactly on upstream PR seconv: add seconv mcp, a Model Context Protocol server over stdio SubtitleEdit/subtitleedit#14129 HEAD ad51c0ae9f5e8942f281e4acd82090974f9b8847
• no tool/protocol behavior changes for valid MCP invocations
• full solution CI pending

AI assistance: ChatGPT was used to audit CLI/MCP argument-parsing parity.