fix: deduplicate soundfont scan + source label + delete only uploads

- _scan_soundfonts: dict-keyed by base_id to prevent duplicates
- Add 'source' field ('system' | 'upload') to each soundfont entry
- Delete endpoint: only allow deleting upload soundfonts (403 for system)
- Frontend: show (system)/(upload) tag, hide Delete for system fonts

app/static/js/app.jsx

@@ -3459,12 +3459,17 @@ const PluginManagerModal = ({ isOpen, onClose, pluginsData }) => {
                       React.createElement('div', { className: 'text-xs font-semibold text-slate-200' }, sf.display || sf.name || sf.id),
                       React.createElement('div', { className: 'text-[10px] text-zinc-500' }, sf.file || sf.name)
                     )
-                  ),
-                  React.createElement('div', { className: 'flex items-center gap-2' },
-                    React.createElement('button', {
-                      onClick: () => setSfToDelete(sf),
-                      className: 'text-[10px] text-zinc-500 hover:text-red-400 opacity-0 group-hover:opacity-100 transition px-2 py-1'
-                    }, 'Delete')
+                  ), React.createElement('div', {
+                    className: 'text-[10px] text-zinc-500'
+                  }, sf.file || sf.name, ' ', React.createElement('span', {
+                    className: sf.source === 'system' ? 'text-blue-400' : 'text-amber-500'
+                  }, sf.source === 'system' ? '(system)' : '(upload)'))
+                ),
+                React.createElement('div', { className: 'flex items-center gap-2' },
+                  sf.source === 'upload' ? React.createElement('button', {
+                    onClick: () => setSfToDelete(sf),
+                    className: 'text-[10px] text-zinc-500 hover:text-red-400 opacity-0 group-hover:opacity-100 transition px-2 py-1'
+                  }, 'Delete') : React.createElement('span', { className: 'text-[10px] text-zinc-700' }, 'System')
                   )
                 )
               )