fix(12-02): move Add Library button inline with scan buttons

Add Library now sits in the same row as Scan and Full Rescan, sharing
the same btn-primary style and size. Removed the standalone button
below the library list.

frontend/src/components/config-page/config-page.ts

@@ -971,11 +971,6 @@ export class ConfigPage extends LitElement {
             );
         }
 
-        .add-library-btn {
-            margin-top: 0.75em;
-            margin-bottom: 1em;
-        }
-
         .toast {
             position: fixed;
             bottom: 80px;
@@ -2291,6 +2286,12 @@ export class ConfigPage extends LitElement {
                               </button>
                           `
                         : html`
+                              <button
+                                  class="btn-primary"
+                                  @click=${this.handleAddLibrary}
+                              >
+                                  Add Library
+                              </button>
                               <button
                                   class="btn-primary"
                                   @click=${this.handleSoftScan}
@@ -2401,13 +2402,6 @@ export class ConfigPage extends LitElement {
                     `
                     : nothing}
 
-                <button
-                    class="btn-primary add-library-btn"
-                    @click=${this.handleAddLibrary}
-                >
-                    Add Library
-                </button>
-
                 <config-field
                     .schema=${{
                         key: 'concurrencyMode',