Omapager becomes the shell's notification engine

ryanrhughes proposed and merged omacom/omarchy#15932 into quattro, folding Omapager into the shell and retiring it as a separate plugin. The replacement supports per-source stacks, snoozing, Do Not Disturb, held and recent notifications, history and notification actions. Cards follow the theme's corner treatment, and website icons are not fetched separately.

The engine stores its history and quiet state locally, with verification codes stored only in redacted form. Related quattro commits attributed to Ryan Hughes remove inline reply and the KDE Connect helper, and read the previous engine's Do Not Disturb setting until the new quiet state is saved. Those changes are recorded in omacom/omarchy@a10f7a10f7ba and omacom/omarchy@e3e08d305052; the merge does not establish stable-release availability.