fix(lockscreen): fix login view disappearing after TTY switch and hotplug

[deepin-wm]

修复：TTY 切回后登录界面消失 & 副屏拔插后登录/电源界面不跟随鼠标

问题

• 场景 A：扩展模式下，切换到其他 TTY 再切回 treeland，登录界面（m_loginView）消失且不再出现。
• 场景 B：扩展模式下拔插副屏后，登录/电源界面不再跟随鼠标显示到副屏。

根因

• Bug A：切换 TTY 时 DRM 输出被禁用再重新启用，QML 场景图可能销毁 m_loginView，但裸指针 QQuickItem* m_loginView 变成悬空指针。
• Bug B：addOutput() 未连接 WOutput::enabledChanged 信号，且未在输出添加后调用 repositionLoginView()，导致热插拔副屏后登录/电源界面不会跟随鼠标。

改动

• m_loginView 从 QQuickItem* 改为 QPointer<QQuickItem>，QML 销毁后自动置 null
• addOutput() 连接 WOutput::enabledChanged → onOutputEnabledChanged（使用 Qt::UniqueConnection），末尾调用 repositionLoginView()
• removeOutput() 断开 enabledChanged 连接
• 新增 onOutputEnabledChanged()：检查 isEnabled() 后，若 m_loginView 为空且可见则重建，否则重新定位
• onCursorPositionChanged()：m_loginView 为空且可见时触发 createLoginView() 重建

Multica Issue

WM-465

Summary by Sourcery

Restore lock-screen login and power interface visibility and mouse-following behavior after TTY switches and display hotplug events.

Bug Fixes:

• Prevent the lock-screen login view from disappearing after TTY switches by safely handling QML view destruction and recreating it when needed.
• Keep login and power interfaces positioned correctly across display hotplug and output enable/disable events.

Enhancements:

• Improve lock-screen output lifecycle handling by updating view positioning whenever outputs are added, enabled, or the cursor moves.

[sourcery-ai]

Reviewer's Guide

Fixes lock-screen login view loss after TTY switching by making its pointer resilient to QML destruction and adding recovery logic, while updating output lifecycle handling so login and power views are repositioned or recreated after display hotplug and re-enablement.

Sequence diagram for lock-screen recovery after output re-enablement

sequenceDiagram
    participant WOutput
    participant LockScreen
    participant QML

    WOutput->>LockScreen: onOutputEnabledChanged()
    alt output disabled
        LockScreen-->>WOutput: return
    else output enabled and login view missing
        LockScreen->>LockScreen: isVisible()
        LockScreen->>QML: createLoginView()
    else output enabled and login view exists
        LockScreen->>LockScreen: repositionLoginView()
    end

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Sequence diagram for login view recovery after cursor movement

sequenceDiagram
    participant Cursor
    participant LockScreen
    participant QML

    Cursor->>LockScreen: onCursorPositionChanged()
    alt login view missing and lock screen visible
        LockScreen->>QML: createLoginView()
    else login view exists
        LockScreen->>LockScreen: repositionLoginView()
    end

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File-Level Changes

Change	Details	Files
Make login-view lifetime safe across QML scene teardown and recreate it when needed.	Replace the raw login-view pointer with QPointer so destruction automatically clears the reference. Recreate the view when cursor movement or output re-enablement occurs while the lock screen is visible and no view exists. Continue repositioning an existing view in response to cursor changes and output state changes.	src/core/lockscreen.cpp src/core/lockscreen.h
Track output hotplug and enablement changes so lock-screen surfaces follow the active display.	Connect each output’s enabledChanged signal with a unique connection. Reposition the login view after adding an output and disconnect the signal when removing one. Ignore disabled or invalid output notifications.	src/core/lockscreen.cpp

Possibly linked issues

• #WM-465: PR replaces the dangling login-view pointer with QPointer, addressing the likely stale QML item behind the rendering crash.

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