Fix Copilot auth detection in macOS release builds

[Redth]

Signed and notarized macOS builds could incorrectly report that the Copilot CLI was missing or that the user was logged out, even when the CLI and auth were already valid. This happens because GUI-launched apps do not inherit the same shell environment as Terminal, so Copilot startup was sometimes running with the wrong PATH/HOME context and stale availability state.

This change hardens the Copilot integration by:

• resolving the CLI from bundled and common macOS install locations instead of relying on the inherited PATH alone
• passing a stable user-scoped environment and writable working directory into the SDK-launched Copilot process
• serializing connect/availability checks to avoid stale or overlapping state during retries
• making the UI "Check Again" path perform a real refresh instead of reusing the first cached failure
• adding focused tests around CLI path resolution and launch environment construction

This is a behavior fix only; no user-facing workflow changes are intended beyond making Connect behave reliably in release builds.