feat(stats): per-device reading breakdown + device attribution on progress syncs

- Attribution: registered clients may now send their device token in
  X-Device-Token on PUT /api/media-items/:id/progress (the user JWT
  stays primary). The token must map to a device OWNED BY the caller —
  foreign/invalid/absent tokens soft-fail to plain web attribution so a
  stats decoration can never break a sync. Attributed pushes capture
  device_id (FK-safe), device_metadata.source = the registered device
  name ('Pixel 9', 'Kindle Paperwhite'), and last_sync surfaces show
  that device. Side effect worth having: app-vs-web pushes used to be
  LWW-invisible (both sources read 'web'); they now surface as
  legitimate cross-source progress conflicts when they diverge.
- /stats gains a By Device panel alongside By Library (grid 3-wide):
  reading minutes + sessions + books per registered device, plus one
  Web / unsynced bucket for device-less pushes so the panel always
  reconciles with the headline totals. Range-aware, family-lens
  scoped; renderBars shared between panels in stats.ts.
- The device identity IS the registered platform: devices rows already
  carry the name/type the client registered (app sends Build.MODEL +
  'mobile' at /api/devices/register, KOReader/Kobo likewise) — no new
  identity plumbing on the server.

Tests: capture attributed to the device (row device_id + source
metadata + last_sync_source), foreign/nonexistent tokens soft-fail,
device buckets reconcile (80 attributed + 75 unsynced = 155 total).
Full suite PASS.

internal/services/statistics_service.go

@@ -114,6 +114,18 @@ type LibraryStats struct {
 	Books     int    `json:"books"`
 }
 
+type DeviceStats struct {
+	// DeviceID is empty for the unattributed bucket (web reader pushes
+	// that carry no device credential) — Name then reads "Web / unsynced".
+	DeviceID string `json:"device_id"`
+	Name     string `json:"name"`
+	Type     string `json:"type"`
+	Minutes  int    `json:"minutes"`
+	Pages    int    `json:"pages"`
+	Sessions int    `json:"sessions"`
+	Books    int    `json:"books"`
+}
+
 type UserSummaryStats struct {
 	Range             string         `json:"range"`
 	Days              int            `json:"days"`
@@ -131,8 +143,9 @@ type UserSummaryStats struct {
 	MostActiveWeekday string         `json:"most_active_weekday"` // by minutes over the range; "" when nothing
 	MostActiveDay     string         `json:"most_active_day"`     // date with the most minutes
 	MostActiveMinutes int            `json:"most_active_day_minutes"`
-	TopBooks          []TopBookStats `json:"top_books"`
-	LibraryBreakdown  []LibraryStats `json:"library_breakdown"`
+	TopBooks         []TopBookStats `json:"top_books"`
+	LibraryBreakdown []LibraryStats `json:"library_breakdown"`
+	DeviceBreakdown  []DeviceStats  `json:"device_breakdown"`
 }
 
 type WeekSummaryStats struct {
@@ -225,6 +238,7 @@ func (s *StatisticsService) UserSummary(ctx context.Context, userID pgtype.UUID,
 		Daily:            make([]DailyStats, 0, statsRange.Days),
 		TopBooks:         []TopBookStats{},
 		LibraryBreakdown: []LibraryStats{},
+		DeviceBreakdown:  []DeviceStats{},
 	}
 
 	// Zero-filled calendar (inclusive of today).
@@ -380,6 +394,38 @@ func (s *StatisticsService) UserSummary(ctx context.Context, userID pgtype.UUID,
 		}
 	}
 
+	// Per-device breakdown in the range (LEFT JOIN devices: NULL-device
+	// pushes aggregate into one unattributed row so the panel reconciles
+	// with the totals).
+	deviceRows, err := s.db.GetUserDeviceBreakdown(ctx, database.GetUserDeviceBreakdownParams{
+		UserID:            userID,
+		StartTime:         pgtype.Timestamptz{Time: statsRange.Start, Valid: true},
+		EndTime:           pgtype.Timestamptz{Time: statsRange.End, Valid: true},
+		VisibleLibraryIds: visibleOrNil(visibleIDs),
+	})
+	if err == nil {
+		for _, row := range deviceRows {
+			entry := DeviceStats{
+				Minutes:  int(row.TotalSeconds) / 60,
+				Pages:    int(row.TotalPages),
+				Sessions: int(row.SessionCount),
+				Books:    int(row.BookCount),
+				Name:     "Web / unsynced",
+				Type:     "unattributed",
+			}
+			if row.DeviceName.Valid && row.DeviceName.String != "" {
+				entry.Name = row.DeviceName.String
+			}
+			if row.DeviceType.Valid && row.DeviceType.String != "" {
+				entry.Type = row.DeviceType.String
+			}
+			if row.ID.Valid {
+				entry.DeviceID = uuid.UUID(row.ID.Bytes).String()
+			}
+			summary.DeviceBreakdown = append(summary.DeviceBreakdown, entry)
+		}
+	}
+
 	return summary, nil
 }