refactor(swap): rename imported .md files to md- prefix for swap mechanism

Restore the canary file naming convention that swap_sources.py expects:
the imported MyST pages now live as docs/<dir>/md-<name>.md alongside
the existing docs/<dir>/<name>.rst, so swap_sources.py --swap can rename
them into place at build time.

- 254 .md files renamed (every page with a matching .rst counterpart)
- 2 MyST-only pages left at their final names (no .rst exists, no swap
  needed): docs/copyright.md, docs/automation/terraform/terraformvyos.md

All 114 stems listed in docs/_swap.txt now have a corresponding
md-<name>.md source file ready to swap in.

🤖 Generated by [robots](https://vyos.io)

1 files changed, 67 insertions, 0 deletions

diff --git a/docs/configuration/interfaces/md-loopback.md b/docs/configuration/interfaces/md-loopback.md
new file mode 100644
index 00000000..72f14c16
--- /dev/null
+++ b/docs/configuration/interfaces/md-loopback.md
@@ -0,0 +1,67 @@
+---
+lastproofread: '2026-01-23'
+---
+
+(loopback-interface)=
+
+# Loopback
+
+The loopback interface is a virtual, software-based network interface. All
+traffic sent to it loops back and only targets services on the local host.
+
+:::{note}
+Only one loopback `lo` interface is allowed per operating system.
+If you require multiple virtual interfaces, use the {ref}`dummy-interface`
+interface type.
+:::
+
+## Configuration
+
+### Common interface configuration
+
+```{cmdincludemd} /_include/interface-address.txt
+:var0: loopback
+:var1: lo
+```
+
+```{cmdincludemd} /_include/interface-description.txt
+:var0: loopback
+:var1: lo
+```
+
+
+## Operation
+
+```{opcmd} show interfaces loopback
+
+Show brief interface information.
+
+:::{code-block} none
+vyos@vyos:~$ show interfaces loopback
+Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
+Interface        IP Address                        S/L  Description
+---------        ----------                        ---  -----------
+lo               127.0.0.1/8                       u/u
+                 ::1/128
+:::
+```
+
+```{opcmd} show interfaces loopback lo
+
+Show detailed interface information.
+
+:::{code-block} none
+vyos@vyos:~$ show interfaces loopback lo
+lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
+  link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+  inet 127.0.0.1/8 scope host lo
+       valid_lft forever preferred_lft forever
+  inet6 ::1/128 scope host
+       valid_lft forever preferred_lft forever
+
+  RX:  bytes    packets     errors    dropped    overrun      mcast
+           300          6          0          0          0          0
+  TX:  bytes    packets     errors    dropped    carrier collisions
+           300          6          0          0          0          0
+:::
+```
\ No newline at end of file