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/querier.go

@@ -359,6 +359,10 @@ type Querier interface {
 	GetUserByEmailOrUsername(ctx context.Context, email string) (GetUserByEmailOrUsernameRow, error)
 	GetUserByUsername(ctx context.Context, username string) (GetUserByUsernameRow, error)
 	GetUserCollectionsForDashboard(ctx context.Context, userID pgtype.UUID) ([]Collections, error)
+	// 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.
+	GetUserDeviceBreakdown(ctx context.Context, arg GetUserDeviceBreakdownParams) ([]GetUserDeviceBreakdownRow, error)
 	// Get user device usage statistics
 	GetUserDeviceUsage(ctx context.Context, userID pgtype.UUID) ([]GetUserDeviceUsageRow, error)
 	GetUserForLogin(ctx context.Context, email string) (GetUserForLoginRow, error)