[Screen Toolkit] Hardcoded /tmp filenames cause cross-user Permission Denied errors on multi-user systems

[wright802]

Environment

• Plugin version: 1.3.3 (minNoctaliaVersion 4.5.0 per manifest.json)
• Distro: CachyOS (Arch-based)
• Compositor: Hyprland
• Setup: 4 separate Linux user accounts on one machine, each with Screen Toolkit enabled independently

Summary
Capture, annotate, copy, save, and share all fail intermittently with a generic
"Screen capture failed" toast
depending on which user account last used the tool — not tied to any one
user's config.

Root cause
Several scripts and QML files write intermediate/output images to fixed,
non-per-user filenames under /tmp, e.g.:

• /tmp/screen-toolkit-annotate.png
• /tmp/screen-toolkit-annotate-pixel.png
• /tmp/screen-toolkit-annotate-zoom.png
• /tmp/screen-toolkit-overlay.png
• /tmp/screen-toolkit-share.png
• /tmp/screen-toolkit-palette.png
• /tmp/screen-toolkit-qr.png

/tmp has the sticky bit set, so only a file's owner (or root) can
overwrite or delete it. On a multi-user system, whichever account used a
given tool most recently ends up owning that shared file — every other
account's next attempt at the same action then fails with a permission
error, since it can neither write over nor delete the existing file.

Evidence
The real error doesn't reach journalctl — Noctalia logs it internally
(readable via qs log -c noctalia-shell):
Failed to open file '/tmp/screen-toolkit-annotate.png' for writing: Permission denied

Where this shows up

• scripts/capture.sh — annotate-window, pin, palette, and qr actions
• Main.qml — the annotateProc/launchAnnotateFullscreen capture paths
• overlays/Annotate.qml — imagePath property and the Copy / Save /
  Save-overlay / Share-flatten flows (roughly 20 references across the
  filenames above)

Steps to reproduce

1. Enable Screen Toolkit on two separate user accounts on the same machine
2. As user A, use annotate/pin/palette/qr/copy/save (any of the above) — succeeds
3. As user B, use the same action — fails with permission denied on the
   collided /tmp file

Suggested fix
Use a genuinely per-user location instead of shared /tmp — e.g.
Quickshell.env("XDG_RUNTIME_DIR") (/run/user/<uid>/, mode 0700,
already exclusive per user) in place of the hardcoded /tmp/... paths.

I patched just the plain-capture path locally (capture.sh +
Main.qml's _grimGeometry flow) using this approach and confirmed it
resolves the collision for that path — happy to share the diff if useful,
though I didn't attempt the much larger Annotate.qml surface myself.

Workaround in the meantime
rm -f /tmp/screen-toolkit-* executed by the last user to capture screen,
then retrying.