feat: drive migration & Tier 2 restic deprecation (v0.18.0)

Phase 1: Deprecate restic as Tier 2 method (rsync only), auto-migrate on startup
Phase 2: Enhanced per-app migration with backup awareness, DB dump copy, auto-cleanup
Phase 3: Full drive migration with decommissioned state, rollback support, wizard UI
Phase 4: Hub report includes decommissioned drive state

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

controller/internal/report/infra_backup.go

@@ -75,12 +75,6 @@ func BuildInfraBackup(
 		logger.Printf("[WARN] Infra backup: could not read restic password file: %v", err)
 	}
 
-	// Cross-drive password is stored as plain text (not base64) because it's
-	// already a string in settings, unlike ResticPassword which comes from a file.
-	if pw := sett.GetCrossDriveResticPassword(); pw != "" {
-		ib.CrossDrivePassword = pw
-	}
-
 	// Collect disk layout from fstab + blkid
 	ib.DiskLayout = collectDiskLayout(systemDataPath)