Re-enable multifile-edit-claude simulation tests with a supported Claude model

[bhavyaus]

The -claude variant in extensions/copilot/test/inline/multiFileEdit.stest.ts was temporarily disabled in #311003 because CHAT_MODEL.CLAUDE_SONNET (claude-3.5-sonnet) now returns model_not_supported from the endpoint, breaking simulation cache regen.

To do

• Update CHAT_MODEL.CLAUDE_SONNET (or pick a different constant) to point at a currently-supported Claude model, e.g. claude-sonnet-4.
• Re-enable the call in multiFileEdit.stest.ts (search for the // Temporarily disabled comment).
• Regenerate the simulation cache for the multifile-edit-claude suite.
• Update the test family name in baseline.json if the model id changes.

Context

• Main currently passes this test only because the salt is old and stale cache entries (from when the model still worked) satisfy simulate-ci --require-cache.
• feat: make stream a caller-controlled passthrough in Messages API #311003 bumped the cache salt and changed request shape (key ordering), invalidating those entries, exposing the underlying model_not_supported error.

Owner: @bhavyaus