[v3DJG6GL]

Summary

This PR adds the option to open the Activities Window with just one mouse click instead of several clicks:

A middle click on the tray icon (StatusNotifierItem SecondaryActivate on Linux, mapped by Qt to QSystemTrayIcon::MiddleClick) opens the Activities Window now directly. A middle click on the tray icon while the window is open hides it again. A minimized window is handled as not shown, a middle click therefore shows the window again.
Other mouse actions are left unchanged.

This would likely be a sufficient compromise for users who were quite unhappy with the removal of the flyout/activity list.

While I also preferred the flyout Nextcloud Desktop had before the v34 release, I think this is a reasonable compromise. Maybe somewhere in the future might be a more UX-friendly implementation added to the codebase... :)

LoC Changes

Type	Code	Comments	Blank	Total
Production	20	1	3	24
Tests	110	8	23	141
Total	130	9	26	165

I can ofc remove some tests if you think that's too much for such a small feature...

Resolves (partially)

Some reports I've found which would be partially resolved by this PR:
#10475
#10515
#10688

Summary

TODO

• Unit tests for the click mapping (TrayActivationPolicyTest) and the show/hide toggle (SystrayActivitiesWindowTest)
• CI tests pass
• Manual test on Linux (Kubuntu v26.04/KDE Plasma)
• Manual test on Windows
• Manual test on macOS (<-- I don't have apple devices and therefore cannot test this plattform!)
• GNOME (+AppIndicator extension)

Checklist

• Sign-off message is added to all commits.
• The commit messages are following The Conventional Commits specification.
• The commit history is clean with no merge commits.
  • How to rebase your commits
  • How to squash commits with rebase
    - [ ] Uploaded screenshots from before and after for UI changes.
• Test(s) added to branch, with before/after results included in PR description, for performance improvements where applicable.
• Documentation has been updated or is not required.
• Backports requested where applicable (critical bugfixes).
• Labels added where applicable (bug/enhancement).
• Milestone added for target version.

AI (if applicable)

• The content of this PR was partly or fully generated using AI
  • I have read the guidelines for AI-assisted contributions.
  • I have read Nextcloud's AI Contribution Policy.

LLM Disclosure

Developed with assistance from Claude Code (Opus 5.5). The LLM helped me identify the related files, code parts and proposed possible code modifications and fixes.
I've reviewed, cleaned, refactored and hardened the code the best I could.