feat: Admin is a left rail with how many wait on you in each queue, and the Overview opens with a verdict, the queues that need you and since when, then the clear ones on one line (M503 #5605)

- GET /api/admin/summary: every admin queue (requests, reported tracks,
  playback errors, duplicates, suspect sources, missing files) with its
  count and the age of its oldest item, in one query.
- The admin layout drops the 11-tab strip for SectionRail, as Settings and
  the Collection have, with each queue's count as its badge; the counts
  refresh on each admin navigation and every 30s.
- The Overview leads with "Nothing needs you." or "N things need you.",
  lists each waiting queue with "oldest 3d ago" and a link to it, counts a
  failed library scan as a problem, and names the empty queues on one line.
  The request and quarantine previews and the stat tiles are gone; those
  queues are worked on their own pages. A failed summary says so with Try
  again instead of reading as all-clear.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/admin_summary.go

@@ -0,0 +1,59 @@
+package api
+
+import (
+	"net/http"
+
+	"github.com/jackc/pgx/v5/pgtype"
+
+	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
+)
+
+// adminQueueView is one queue that waits on a person: how many, and since
+// when the oldest of them has waited (null when the queue is empty).
+type adminQueueView struct {
+	Count int64   `json:"count"`
+	Since *string `json:"since"`
+}
+
+// adminSummaryView is what the admin rail and the Overview's verdict read
+// (#5605): every queue an admin acts on, in one response, so each admin page
+// pays one cheap read for its rail.
+type adminSummaryView struct {
+	Requests       adminQueueView `json:"requests"`
+	Quarantined    adminQueueView `json:"quarantined"`
+	PlaybackErrors adminQueueView `json:"playback_errors"`
+	Duplicates     adminQueueView `json:"duplicates"`
+	Suspect        adminQueueView `json:"suspect"`
+	Missing        adminQueueView `json:"missing"`
+}
+
+func queueView(count int64, since pgtype.Timestamptz) adminQueueView {
+	v := adminQueueView{Count: count}
+	if count > 0 && since.Valid {
+		s := formatTimestamp(since)
+		v.Since = &s
+	}
+	return v
+}
+
+func adminSummaryFrom(row dbq.AdminSummaryRow) adminSummaryView {
+	return adminSummaryView{
+		Requests:       queueView(row.Requests, row.RequestsSince),
+		Quarantined:    queueView(row.Quarantined, row.QuarantinedSince),
+		PlaybackErrors: queueView(row.PlaybackErrors, row.PlaybackErrorsSince),
+		Duplicates:     queueView(row.Duplicates, row.DuplicatesSince),
+		Suspect:        queueView(row.Suspect, row.SuspectSince),
+		Missing:        queueView(row.Missing, row.MissingSince),
+	}
+}
+
+// handleGetAdminSummary implements GET /api/admin/summary.
+func (h *handlers) handleGetAdminSummary(w http.ResponseWriter, r *http.Request) {
+	row, err := dbq.New(h.pool).AdminSummary(r.Context())
+	if err != nil {
+		h.logger.Error("admin: summary", "err", err)
+		writeAdminJSONErr(w, http.StatusInternalServerError, "server_error")
+		return
+	}
+	writeJSON(w, http.StatusOK, adminSummaryFrom(row))
+}