D-Bus Phase 3/4: upgrade sessiond, services, add StatusNotifierWatcher, consolidate configs

- redbear-sessiond: add Manager.Inhibit (pipe FD), CanPowerOff/CanReboot/
  CanSuspend/CanHibernate/CanHybridSleep/CanSleep (return na), PowerOff/
  Reboot/Suspend stubs, GetSessionByPID, ListUsers, ListSeats,
  ListInhibitors, ActivateSession/LockSession/UnlockSession/TerminateSession
- redbear-sessiond: add Session SetIdleHint, SetLockedHint, SetType,
  Terminate methods; wire PauseDevice/ResumeDevice/Lock/Unlock signal
  emission via SignalEmitter injection; add dynamic device enumeration
  scanning /scheme/drm/card* and /dev/input/event* at startup
- redbear-sessiond: replace infinite pending() with stoppable shutdown
  via tokio watch channel + control socket shutdown command
- redbear-upower: add Changed signal emission with 30s periodic polling
  and power state snapshot comparison
- redbear-notifications: add ActionInvoked signal, expand capabilities
  to body + body-markup + actions
- redbear-polkit, redbear-udisks: replace pending() with stoppable
  shutdown via signal handling + watch channel
- Add redbear-statusnotifierwatcher: new session bus service implementing
  org.freedesktop.StatusNotifierWatcher for KDE system tray
- Add D-Bus activation file for StatusNotifierWatcher
- KWin session.cpp: try LogindSession before NoopSession fallback
- Consolidate config profiles: remove obsolete redbear-desktop, redbear-kde,
  redbear-live-*, redbear-minimal-*, redbear-wayland configs; simplify
  to three supported targets (redbear-full, redbear-mini, redbear-grub)
- Update DBUS-INTEGRATION-PLAN.md and DESKTOP-STACK-CURRENT-STATUS.md
  with Phase 3/4 fragility assessment, KWin readiness matrix, and
  completeness gap analysis

local/docs/USB-VALIDATION-RUNBOOK.md

@@ -126,13 +126,12 @@ In-guest quick checks:
 
 ## Compile-target note
 
-Red Bear has exactly four compile targets:
+Red Bear has exactly three compile targets:
 
 - `redbear-mini`
-- `redbear-live-mini`
 - `redbear-full`
-- `redbear-live-full`
+- `redbear-grub`
 
-Older names such as `redbear-desktop`, `redbear-wayland`, `redbear-kde`, and `redbear-minimal` may
-still appear in historical notes or implementation details, but they are not the supported
-compile-target surface.
+Older names such as `redbear-desktop`, `redbear-wayland`, `redbear-kde`, `redbear-minimal`,
+`redbear-live-mini`, and `redbear-live-full` may still appear in historical notes or
+implementation details, but they are not the supported compile-target surface.