fix: visible Save/Cancel buttons on AgentHealth config edit mode

Replace subtle Unicode checkmark/X with proper labeled buttons styled
as primary (Save) and secondary (Cancel) for better visibility.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -565,8 +565,10 @@ export default function AgentHealth() {
                   <span>{configDraft.metricsEnabled ? 'On' : 'Off'}</span>
                 </label>
               </div>
-              <button className={styles.configEditBtn} title="Save" onClick={saveConfigEdit} disabled={updateConfig.isPending}>&#x2713;</button>
-              <button className={styles.configEditBtn} title="Cancel" onClick={() => { setConfigEditing(false); setConfigDraft({}); }}>&#x2715;</button>
+              <div className={styles.configActions}>
+                <button className={styles.configSaveBtn} onClick={saveConfigEdit} disabled={updateConfig.isPending}>Save</button>
+                <button className={styles.configCancelBtn} onClick={() => { setConfigEditing(false); setConfigDraft({}); }}>Cancel</button>
+              </div>
             </>
           ) : (
             <>