Redesign dashboard: refined-minimal layout with product thumbnails

Move the dashboard from boxed glass cards to an airy, hairline-separated
layout where type and whitespace carry the page, then surface listing
images as the visual anchor.

- Solid surfaces (drop backdrop-filter glass, per spec); calm flat field
  with a single cool top-glow replacing the drifting aurora and dot-grid.
- Recent results / recent alerts are now product feeds with 52px
  thumbnails, listing titles, and price; image_url threaded through
  ResultRow/AlertRow (data already stored, just unsurfaced).
- ListResults gains an OnlyAlerted filter so the alerts panel reuses its
  decryption path instead of a raw query.
- Dashboard recent results capped at 8 for a balanced snapshot.

internal/db/queries.go

@@ -791,6 +791,8 @@ type ResultsQuery struct {
 	// Exception: yahoo-auctions-jp is auction-only — NULL ends_at there means
 	// the actor's ending_date didn't parse, and those rows are also dropped.
 	ExcludeEnded bool
+	// OnlyAlerted restricts to rows that triggered a deal alert.
+	OnlyAlerted bool
 }
 
 func (s *Store) ListResults(ctx context.Context, q ResultsQuery) ([]models.Result, error) {
@@ -817,6 +819,9 @@ func (s *Store) ListResults(ctx context.Context, q ResultsQuery) ([]models.Resul
 		conds = append(conds, `((ends_at IS NULL AND source != 'yahoo-auctions-jp') OR ends_at > ?)`)
 		args = append(args, time.Now().UTC())
 	}
+	if q.OnlyAlerted {
+		conds = append(conds, `alerted = 1`)
+	}
 	where := ""
 	if len(conds) > 0 {
 		where = `WHERE ` + strings.Join(conds, ` AND `)