fix: avoid signal-handler deadlocks during session shutdown

[yixinshark]

POSIX signal handlers called SessionManager::doLogout(), which invokes Qt/D-Bus while interrupted code may hold their locks. Remove those handlers and retain crash/termination cleanup through the existing ExecStopPost and OnFailure systemd paths. Also remove the obsolete dde-dock.service stop call: the current Dock is dde-shell@DDE.service.

Desktop and Dock start independently. The paired tray target owns its ordering after the Dock; this PR adds no desktop-before-Dock or Dock-before-desktop constraint. Update the lifecycle document to match the current services.

移除信号处理函数中不安全的 Qt/D-Bus 调用，保留 systemd 对正常及异常退出的清理。删除旧 dde-dock 调用，保持桌面与 Dock 并行启动，并更新生命周期说明。

Validation

• Qt6 build and existing CTest: 1/1 passed.
• Systemd lifecycle fixtures with the paired tray change passed: parallel desktop/Dock startup, replacement-Dock restart, cancellation/failure recovery and shutdown ordering.
• Repeated deployed login/logout checks on X11: latest five tray stops took 41–67 ms, and Dock stops took 20–36 ms. These are individual service stop times, not total logout latency.
• Native Wayland logout remains unverified. The separately observed greeter wallpaper/DConfig teardown stall and window remnants are not addressed here.

Paired change: linuxdeepin/dde-tray-loader#523

Pms: BUG-378589

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: yixinshark

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

The PR removes reentrant Qt/D-Bus signal handlers and the obsolete direct dock stop, delegating cleanup to systemd, and revises unit dependencies so the dock stops before the desktop while tray shutdown can proceed in parallel. Review the service ordering carefully alongside the companion dde-tray-loader change, and verify both startup synchronization and shutdown behavior.

Sequence diagram for systemd-managed session logout

sequenceDiagram
    participant Systemd
    participant SessionManager
    participant Dock
    participant Desktop

    Systemd->>SessionManager: stop
    SessionManager->>SessionManager: prepareLogout(force)
    Note over SessionManager: systemd retains ExecStopPost cleanup
    Systemd->>Dock: stop
    Dock-->>Systemd: stopped
    Systemd->>Desktop: stop
    Desktop-->>Systemd: stopped

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File-Level Changes

Change	Details	Files
Eliminate unsafe logout-time signal handling and rely on systemd-managed cleanup.	Remove SIGINT/SIGABRT/SIGTERM/SIGSEGV handlers that invoked Qt/D-Bus logout logic from signal context. Remove signal-handler initialization and related declarations/includes. Remove the direct legacy dde-dock.service stop operation and its service constant. Preserve the existing systemd ExecStopPost cleanup path.	src/dde-session/impl/sessionmanager.cpp src/dde-session/impl/sessionmanager.h src/utils/utils.h
Adjust systemd shutdown ordering so the shell/dock is stopped before the desktop without unnecessarily serializing tray shutdown.	Update the shell service dependency/order configuration to stop dde-shell@DDE.service before the desktop. Remove direct ordering against the tray target while retaining companion tray readiness synchronization. Update session-manager unit configuration supporting the revised lifecycle ordering.	systemd/dde-session-core.target.wants/dde-shell@DDE.service systemd/dde-session-manager.service.in

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