fix(privacy-indicator): use StdioCollector to read camera detection output

[cyril-marpaud]

Problem

Camera detection was not working on Ubuntu. Process.stdout in Quickshell is not a string property — it expects a parser object. Reading stdout in onExited always returned nothing, so camActive stayed false.

Fix

Replace the onExited handler with a StdioCollector on the stdout property, reading the output via this.text in onStreamFinished.

Notes

• Tested on Ubuntu with Quickshell 0.2.1 — camera now detected correctly
• The old approach apparently worked on NixOS (different Quickshell version?), but this fix aligns with the documented API
• I have not been able to test on NixOS
• This was vibe-coded, please review carefully

[github-actions]

@Ly-sec - this PR modifies your plugin. Please review when you have a chance.

[Ly-sec]

Looks good to me, merged it :)