When the auto-compile path in handleRun() finishes without producing a
compiledProgram, the previous code dropped the failure on the floor with
only a `console.warn` — the user clicked Run, nothing happened, and they
had no idea why. The accompanying comment also promised "always start
even if compiledProgram is empty" but the code did the opposite.
This commit replaces the dead comment + silent warn with a top-level
error toast + addLog entry, with a different copy for MicroPython mode
(suggests "click Load MicroPython to retry") vs Arduino C++ mode
(directs the user to the output console for the underlying error).
handleCompile already writes the actual cause to the compile-output
console via addLog — this fix just makes sure the user knows their
click failed and where to look.
2f60e3816a