feat(ui): add result highlighting and remove window shadow

Highlighting:
- Dynamic plugin results (calculator, converter, websearch, filesearch)
  get a subtle accent left-border + background tint when auto-detected
- Exact name matches (case-insensitive) are highlighted the same way
- Exact match on apps gets a higher score boost (50k) than other
  providers (30k), so apps rank first when names match exactly

Shadow:
- Removed hardcoded box-shadow from all theme CSS files
- Added --owlry-shadow variable in base.css (defaults to none)
- Themes can opt into shadow via --owlry-shadow if desired

CSS class: .owlry-result-highlight on ResultRow

data/themes/owl.css

@@ -33,8 +33,6 @@
 .owlry-main {
     background-color: rgba(26, 27, 38, 0.95);
     border: 1px solid rgba(65, 72, 104, 0.6);
-    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.5),
-                0 0 0 1px rgba(224, 175, 104, 0.1);
 }
 
 .owlry-search {