PERF.18 CadCraft Studio start-up time: a startup log with timestamps in the desktop shell, measured on Windows and macOS

Not measurable on the VPS (Studio is a Windows/macOS/Linux desktop shell around the web apps; the page part is PERF.1 to PERF.4). KICKOFF line 196 already asks for a startup log a person can send. Plan: desktop-shell logs timestamps for process start, single-instance lock, window shown, first page request, app module running, first drawing paint; the About dialog shows the last start's total; owner measures a cold and a warm start on the Windows workstation and the Mac mini with the 0.9 build and records them in the release notes. Budget: window in under 1 s, app usable in under 3 s warm.