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, 27 insertions, 0 deletions

diff --git a/docs/configuration/system/md-proxy.md b/docs/configuration/system/md-proxy.md
new file mode 100644
index 00000000..286e835f
--- /dev/null
+++ b/docs/configuration/system/md-proxy.md
@@ -0,0 +1,27 @@
+(system-proxy)=
+
+# System Proxy
+
+Some IT environments require the use of a proxy to connect to the Internet.
+Without this configuration VyOS updates could not be installed directly by
+using the {opcmd}`add system image` command ({ref}`update_vyos`).
+
+```{cfgcmd} set system proxy url \<url\>
+
+Set proxy for all connections initiated by VyOS, including HTTP, HTTPS, and
+FTP (anonymous ftp).
+```
+```{cfgcmd} set system proxy port \<port\>
+
+Configure proxy port if it does not listen to the default port 80.
+```
+```{cfgcmd} set system proxy username \<username\>
+
+Some proxys require/support the "basic" HTTP authentication scheme as per
+{rfc}`7617`, thus a username can be configured.
+```
+```{cfgcmd} set system proxy password \<password\>
+
+Some proxys require/support the "basic" HTTP authentication scheme as per
+{rfc}`7617`, thus a password can be configured.
+```
\ No newline at end of file