Pin focused upstream MessagePort contracts

[wieslawsoltes]

Problem and change

The Worker stack needs unchanged upstream coverage for MessageChannel delivery, invalid self-transfer, close behavior, and delivery already queued before close().

This layer pins three upstream WPT files at revision 2c705104a295c48053eeddf7fe0170d790a4e853, records their hashes, and adds them to the Aureon candidate profile:

• webmessaging/message-channels/basics.any.js;
• webmessaging/Channel_postMessage_clone_port_error.any.js;
• webmessaging/message-channels/close.any.js.

Focused cumulative-head results:

• MessageChannel basics: 1/1 assertions;
• MessagePort self-transfer clone error: 1/1 assertions;
• MessagePort close and queued-delivery behavior: 6/6 assertions;
• project Worker/iframe contracts: 5/5 documents, 27/27 assertions;
• worker/MessagePort hybrid throughput and bounds filter: passed;
• iframe Inspector detach filter: passed;
• git diff --check: passed.

Stack: #172 -> #173 -> #174 -> #175. This is layer 4 of 4, based on #174 and is the cumulative validation head. Merge the stack in dependency order only after its focused remote gates pass.

Advances #81 and #108. Both issues remain open for rebuilt packaged Monaco and browser-extension acceptance.