fix: keep the sidebar agent status tag visible on any row

[vanvasten]

Summary

• The agent status tag in a sidebar row (working, done, error, idle) now sits on its own translucent capsule with a thin glass-style rim. Before, its colour could match the selected row's fill or the wallpaper behind the glass and the tag vanished.
• The idle tint uses the secondary colour so it stays readable on the new backing.

Testing

• No automated test: this is a visual change with no behavior to assert. CI builds it.
• Not checked by eye yet; needs a tagged build over a few wallpapers and a selected row.

Demo Video

• Video URL or attachment: needed from the author (visual change).

Checklist

• Tested via CI and, for UI or behavior changes, a tagged build (./scripts/reload.sh --tag <name>)
• I added or updated tests for behavior changes
• I updated docs/changelog if needed
• I requested bot reviews after my latest commit
• All code review bot comments are resolved
• All human review comments are resolved