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/database/queries/queries.sql

@@ -1563,6 +1563,29 @@ SELECT EXISTS(
     WHERE id = sqlc.arg('device_id') AND user_id = sqlc.arg('user_id')
 ) AS has_device;
 
+-- Per-device reading breakdown for a range. LEFT JOIN so pushes that
+-- carry no device (web reader until it identifies) still appear as one
+-- "unattributed" bucket — device minutes must reconcile with the totals.
+-- name: GetUserDeviceBreakdown :many
+SELECT
+    d.id,
+    d.device_name,
+    d.device_type,
+    COUNT(*)::int AS session_count,
+    SUM(COALESCE(rh.time_spent_seconds, 0))::int AS total_seconds,
+    SUM(COALESCE(rh.pages_read, 0))::int AS total_pages,
+    COUNT(DISTINCT rh.media_item_id)::int AS book_count
+FROM reading_history rh
+JOIN media_items mi ON mi.id = rh.media_item_id
+LEFT JOIN devices d ON d.id = rh.device_id
+WHERE rh.user_id = sqlc.arg('user_id')
+  AND COALESCE(rh.reading_session_end, rh.created_at) >= sqlc.arg('start_time')
+  AND COALESCE(rh.reading_session_end, rh.created_at) <= sqlc.arg('end_time')
+  AND (sqlc.narg('visible_library_ids')::uuid[] IS NULL OR mi.library_id = ANY(sqlc.narg('visible_library_ids')::uuid[]))
+GROUP BY d.id, d.device_name, d.device_type
+ORDER BY total_seconds DESC;
+
+
 
  -- ============================================
 -- DEVICE MANAGEMENT & AUTH