Bound WebSocket text stdin lines and document binary fallback

[ryanfowler]

Summary

• Cap WebSocket text/auto stdin lines at 16 MiB before a newline
• Return a clear error that points users to --ws-message-mode binary for raw streams
• Add unit coverage for the overflow case, CRLF handling at the limit, and binary chunk streaming
• Document the stdin limit in the WebSocket docs and CLI reference

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo test --all-features --test cli --test formatting --test grpc --test http --test network --test terminal --test update --test websocket -- --test-threads=1