fix(web-ui): agent companion pet tap vs drag; persist turns only on quit

[GCWing]

Summary

• Desktop pet: Distinguish a short primary click (show main window via \show_main_window) from dragging the pet to move the window, using a small movement threshold and pointer capture.
• Window close / tray: Call \saveAllInProgressTurns\ only when the user actually quits, not when the main window is hidden to tray or macOS dock. Hiding had been settling in-flight turns and clearing Agent companion desktop bubbles prematurely.
• Docs: Clarify in \PersistenceModule\ that \saveAllInProgressTurns\ is for process exit, not for hide-to-tray.

Testing

• Manual: click pet without moving → main window shows.
• Manual: drag pet past threshold → window moves as before.
• Manual: hide main window to tray/dock with active bubbles → bubbles remain until next chat update.
• Manual: quit from close dialog → in-progress turns still persisted.