applets/systemtray: Disambiguate Electron/Chromium tray icons

Summary

All Electron/Chromium-based apps register their system tray icons using the same SNI Id (chrome_status_icon_1). This causes per-app visibility settings (Shown/Hidden/Auto) to be shared — changing one app affects all others.

This MR resolves each SNI item's owning process via D-Bus PID lookup and parses /proc/PID/cmdline to extract the actual app name, then appends it to the config key for disambiguation.

How it works

• Apps with their own binary (1Password, Feishin): /proc/PID/comm already returns a unique name
• Apps using system Electron (Element, Vesktop, Bitwarden): /proc/PID/comm returns electron for all. Instead, the .asar path from cmdline is parsed (/usr/lib/vesktop/app.asar → vesktop)

Config key example: chrome_status_icon_1@vesktop

Resolved bugs

This fixes Bug 470840 (previously closed as RESOLVED UPSTREAM) and its 9 duplicates:

• Bug 468319
• Bug 492846
• Bug 494526
• Bug 498662
• Bug 500238
• Bug 503447
• Bug 507676
• Bug 510948
• Bug 515028

While Electron addressed this upstream in v40+, many apps still use older Electron versions. This KDE-side fix works regardless of the Electron version.

Test plan

• Launch multiple Electron apps (Element, Vesktop, Bitwarden, 1Password, Feishin)
• Open System Tray Settings → Entries
• Each app appears as a separate entry
• Changing visibility of one app does not affect others
• Settings persist after reboot