Add pause controls and menu icons

[alvst]

What changed

• Add pause/resume controls for clipboard capture in Pesty's menu bar and bar menu.
• Reflect paused state with clear status and menu icons.

Why

Users can temporarily stop collection without quitting Pesty and can see that state at a glance.

Validation

• swift build
• swift build -Xswiftc -DMAS
• Tested on Apple Silicon. Intel Mac testing was not available.

Screenshots

Activate Pause

Paused

Menubar Paused

[momenbasel]

Closing as superseded by #39, which is now merged. It adds the same ClipboardMonitor pause flag and status-item icon swap, plus a Cmd-Shift-P binding while the bar is open. Thanks for getting there first - the merged version covers this ground.