docs: propose native tool pattern matching

[Konstantinov-Innokentii]

Proposal

• Put match.argument and match.cases directly inside a tool definition.
• Let a tool match one required string argument without a dynamic resolver.
• Check cases from top to bottom; _ is the required final fallback.
• Show email-domain matching and a conservative Bash example with exact commands.
• Keep the first version small: literal text and the * wildcard only.

Open decision

The proposal does not define the built-in meaning of internal. That needs a separate decision about who counts as internal.

Scope

Documentation only. This syntax is not implemented.