fix: Use Team-ID-prefixed App Group to avoid macOS Sequoia+ TCC prompt

macOS 15 (Sequoia) added an authorization prompt — "would like to
access data from other apps" — for any non-sandboxed Developer-ID-
signed app that accesses an App Group container whose identifier
doesn't follow one of these forms:

  - <TEAMID>.<bundle-id>
  - or, app distributed via the Mac App Store / TestFlight 15.1+
  - or, app's claim to the group is authorized by an embedded
    provisioning profile

CCSwitcher's existing `group.me.xueshi.ccswitcher` identifier failed
all three checks. Every launch, the first call into
`FileManager.containerURL(forSecurityApplicationGroupIdentifier:)`
inside `WidgetData.save()` blocked for several seconds while macOS
displayed the prompt; users on macOS 26 (Tahoe) saw it on every
Sparkle update because the cdhash changes invalidate the prior grant.

Renaming to `584KQTRF3B.me.xueshi.ccswitcher` uses the Team-ID-prefix
form which is auto-authorized and bypasses the prompt entirely.

Migration impact: the only payload in the App Group container is
`widget-data.json`, a transient usage snapshot rebuilt every 5 min,
so users see an empty widget for one refresh cycle then it repopulates
in the new container. No persistent user data is affected.