Show a clear message when a debug run rejects a second browser tab

When a web project is run from Studio with the debugger attached, the host deliberately supports one browser session at a time. Opening the app's address in a second tab during a debug run is therefore rejected — but the tab currently shows the generic status "The application is currently at capacity. Retrying…", which is the same wording used when a published application genuinely reaches its session limit. It reads as if something is wrong or a setting needs changing.

Improve the debug-run case with a clear, specific message, for example: "Debug runs support one browser session. Close this tab, or run without debugging to use multiple sessions." Published applications and ordinary Run (no debugger) keep the existing capacity wording, since there it is accurate.

Expected outcome: a user who opens a second tab during a debug run immediately understands why the tab is not loading and what to do about it.