Feature/tray order

[Carltoffel]

Deterministic and Configurable Tray Icon Ordering

This PR adds a new feature to the Waybar tray module: stable and user-configurable ordering of tray icons.

Problem

Before this change, tray icons were shown in the order in which applications registered themselves via D-Bus. This caused several issues:

• The order depended on application start timing
• Icons could appear in a different order after each login
• Multiple monitors could show different tray orders
• Restarting Waybar often shuffled the tray randomly

There was no reliable way to control or stabilize this behavior.

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What this PR adds

1. Stable default behavior

Even without any configuration, tray icons are now sorted deterministically in alphabetical order based on an internal key (sort_key).

This ensures that:

• Tray order is consistent across all monitors
• Order does not depend on application start timing
• Restarting Waybar keeps the same layout

2. New user configuration options

Users can now explicitly define their preferred tray order using a simple list:

"tray": {
  "order": [
    "vesktop",
    "signal desktop"
  ],
  "order-unknown": "after"
}

• order allows specifying tray icons in the exact desired order
• Items not listed are sorted alphabetically
• order-unknown controls whether unconfigured items appear before or after configured ones

Available keys can be easily discovered via log messages like:

tray: item key='<KEY>' ...

3. Improved handling of Electron apps

Many Electron-based applications register generic tray IDs such as chrome_status_icon_1.
This PR improves that by:

• Deriving a meaningful key from the tooltip text
• Using that key consistently for sorting

This makes it possible to reliably sort apps like Signal, Vesktop, etc.

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How it works internally

• Each tray item now provides a stable sort_key

• The SNI Host component performs centralized reordering

• Reordering is triggered automatically when an item identity becomes available

• Sorting priority is:

  1. Items listed in the user-defined order
  2. All other items alphabetically
  3. Stable tie-break using insertion sequence

This guarantees deterministic results across all Waybar instances.

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Differences to PR #4643

This implementation differs significantly from PR #4643:

• Configuration uses a simple ordered list instead of numeric priorities
• Provides deterministic alphabetical ordering by default
• Sorting is triggered directly when item identity becomes known
• Includes explicit support for Electron app quirks
• Adds user-friendly logging to discover available keys

Overall, this approach focuses on simplicity and predictable behavior.

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Personal note

I want to mention explicitly that I have very limited experience with C++.
This feature was created almost entirely with the help of ChatGPT, which guided me through the design, refactoring, and implementation process step by step.

Feedback and suggestions are very welcome!