fix(ui): center button label text (#925)

* fix(ui): center button label text

.btn was inline-flex with align-items:center but no justify-content, so
buttons wider than their content (min-width / flex:1) rendered the label
left-aligned — visible on the Advanced Search button (min-width 100).

* docs(changelog): centered button label (#925)

CHANGELOG.md

@@ -324,6 +324,14 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Fixed
 
+### Advanced Search — centered button label
+
+**By [@Psychotoxical](https://github.com/Psychotoxical), PR [#925](https://github.com/Psychotoxical/psysonic/pull/925)**
+
+* The **Search** button's label is now centered. Buttons wider than their text (the Search button has a fixed minimum width) previously rendered the label left-aligned.
+
+
+
 ### Radio — track info in OS media controls
 
 **By [@Psychotoxical](https://github.com/Psychotoxical), reported by agriffit79 on GitHub, PR [#924](https://github.com/Psychotoxical/psysonic/pull/924)**

src/styles/themes/button-variants.css

@@ -2,6 +2,7 @@
 .btn {
   display: inline-flex;
   align-items: center;
+  justify-content: center;
   gap: var(--space-2);
   padding: var(--space-2) var(--space-4);
   border-radius: var(--radius-md);