Dashboard detail, library filtering/pagination, simplified playlist times,

job descriptions

Dashboard: format breakdown (FLAC/MP3/etc. counts), approximate library
size (bitrate*length/8, same approximation `beet stats` itself uses --
verified to match its "100.5 GiB" output exactly against the real
library), and a credential auth-state summary per scope (configured y/n
plus, for Bandcamp, cookie expiry parsed locally from the stored cookie
jar -- deliberately not a live network probe like pipeline-status.sh's
Qobuz check, since this renders on every dashboard load).

Library: was one unfiltered page dumping all 4072 tracks. Added search
(artist/title/album), playlist and format filter dropdowns, and real
SQL-level pagination (LIMIT/OFFSET, not fetch-everything-then-slice).
beets_service gained count_items()/distinct_formats() to support this.

Playlists: cron_expr is still the stored/scheduled representation, but the
UI now shows and edits a plain daily time picker instead of raw cron
syntax -- every playlist schedule today is a simple daily HH:MM anyway.
playlist_service.cron_to_time()/time_to_cron() convert at the router
boundary; verified round-trip against all real playlist cron values.

Jobs: each maintenance job now shows a short one-line description of what
it actually does (MAINTENANCE_JOB_DESCRIPTIONS), and "next run" is
formatted consistently with playlists' time style (HH:MM, with a day
qualifier for non-today runs -- maintenance jobs can be weekly/monthly,
unlike playlists' plain daily schedule).

Verified end-to-end against the real production data (4072 tracks, 100.5
GiB, real credentials): stats/format-breakdown/search/pagination all
correct, all 7 credential scopes report configured with Bandcamp's real
cookie expiry (325 days), and a full authenticated page-render sweep
(dashboard, library with every filter combination, playlist detail,
jobs) all returned 200 with no template errors.

app/templates/jobs/index.html

@@ -15,9 +15,12 @@
     <tbody>
       {% for job in maintenance_jobs %}
       <tr>
-        <td class="mono">{{ job.job_key }}</td>
+        <td>
+          <div class="mono">{{ job.job_key }}</div>
+          {% if job.description %}<div class="muted" style="font-size:0.8em; margin-top:0.15rem;" title="{{ job.description }}">{{ job.description }}</div>{% endif %}
+        </td>
         <td>{% if job.enabled %}<span class="badge badge-success">enabled</span>{% else %}<span class="badge badge-muted">disabled</span>{% endif %}</td>
-        <td class="muted">{{ job.next_run or "—" }}</td>
+        <td class="muted mono">{{ job.next_run }}</td>
         <td class="actions-cell">
           <form method="post" action="/jobs/{{ job.job_key }}/run" class="inline">
             <button type="submit" class="btn btn-sm">Run now</button>