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, 16 insertions, 0 deletions

diff --git a/docs/configuration/system/md-sysctl.md b/docs/configuration/system/md-sysctl.md
new file mode 100644
index 00000000..90434fb2
--- /dev/null
+++ b/docs/configuration/system/md-sysctl.md
@@ -0,0 +1,16 @@
+(sysctl)=
+
+# Sysctl
+
+:::{note}
+This page is a stub and needs expansion. Contributions
+welcome via the [VyOS documentation repository](https://github.com/vyos/vyos-documentation).
+:::
+
+This chapter describes how to configure kernel parameters at runtime.
+
+`sysctl` is used to modify kernel parameters at runtime. The parameters
+available are those listed under /proc/sys/.
+
+```{cfgcmd} set system sysctl parameter \<parameter\> value \<value\>
+```
\ No newline at end of file