feat(settings): scan from Settings, and watch every job in place

Scanning goes back where libraries are managed -- the Jobs tab's own
comment said the per-library controls had been taken out of Settings to
build it. "Scan All" and "Full Rescan" join "Add Library", "Scan now"
joins the per-library overflow menu beside Rename and Remove, and a
library being scanned says so where its track count goes.

Each surface then gets the job rows for its own kind: scans under
Libraries, index and enrichment under Search Index, downloads under the
download clients, and the autotag apply in the Autotag view -- where
stopping a run matters most, since applying rewrites tags on disk and
that view had no cancel at all.

The autotag panel shares the header's grid row through a wrapper rather
than taking a third row: it is display:none while nothing is applying,
which is nearly always, and a grid row would still spend the
container's gap on it.

The Launch Page select is derived from `VIEW_META` instead of listing
its ten options, since removing a destination is exactly the change
that leaves two hand-written copies disagreeing.

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

@@ -22,6 +22,7 @@ import { compact } from '@utils/binding';
 import { describeError, explainError } from '@utils/describe-error';
 import { confirmAction } from '@components/confirm-dialog/confirm-dialog';
 import './config-section';
+import '@components/jobs/job-panel';
 import { pickDirectory } from '../../utils/pick-directory';
 
 /**
@@ -274,6 +275,17 @@ export class DownloadClients extends LitElement {
                             </wa-button>
                         </div>
                     `}
+
+                <!--
+                  The Downloads view already shows every download's
+                  lifecycle state; what it has never had is pause,
+                  cancel and the log, which the Jobs tab carried (#27).
+                  Renders nothing while nothing is downloading.
+                -->
+                <job-panel
+                    kinds="download"
+                    heading="Downloads in progress"
+                ></job-panel>
             </config-section>
 
             <config-section