topology: add bcachefs-2copy; add bcachefs-single; rename single->btrfs-single; update planner, fs mapping, CLI, defaults, preview topo strings, README

src/orchestrator/run.rs

@@ -341,9 +341,11 @@ fn build_summary_json(disks: &[Disk], plan: &partition::PartitionPlan, cfg: &Con
 
     // Decide filesystem kinds and planned mountpoints (template) from plan + cfg.topology
     let topo_str = match cfg.topology {
-        crate::types::Topology::Single => "single",
+        crate::types::Topology::BtrfsSingle => "btrfs_single",
+        crate::types::Topology::BcachefsSingle => "bcachefs_single",
         crate::types::Topology::DualIndependent => "dual_independent",
         crate::types::Topology::SsdHddBcachefs => "ssd_hdd_bcachefs",
+        crate::types::Topology::Bcachefs2Copy => "bcachefs_2copy",
         crate::types::Topology::BtrfsRaid1 => "btrfs_raid1",
     };