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, 45 insertions, 0 deletions

diff --git a/docs/contributing/md-cla.md b/docs/contributing/md-cla.md
new file mode 100644
index 00000000..01323111
--- /dev/null
+++ b/docs/contributing/md-cla.md
@@ -0,0 +1,45 @@
+---
+lastproofread: '2025-12-05'
+---
+
+(cla)=
+
+# Contributor License Agreement
+
+Before we can accept your contributions to VyOS, you must sign a **Contributor
+License Agreement (CLA)**.
+
+This is a standard open-source practice that protects both you and the project.
+
+The process is straightforward and fully automated:
+
+1. **Review the CLA document**
+
+   Find the CLA text in our
+   [GitHub repository](https://github.com/vyos/vyos-cla-signatures/).
+
+2. **Submit a pull request**
+
+   When you open a pull request, a CLA bot automatically checks whether all
+   commit authors have signed the CLA.
+
+3. **Follow the bot's instructions**
+
+   If the CLA has not been signed, the bot leaves a comment with instructions.
+   Reply to that comment with the suggested text to sign the CLA.
+
+4. **Wait for confirmation**
+
+   The CLA bot verifies your response and updates the pull request status.
+   Once all commit authors have signed, the bot confirms that the CLA
+   requirement is met and unlocks the pull request for merging.
+
+:::{note}
+Each commit author must sign the CLA.
+
+If your pull request includes commits from multiple contributors, each one
+must sign the CLA before the pull request can be accepted.
+:::
+
+Once you sign the CLA, it remains valid for all your past and future
+contributions to VyOS under the same GitHub identity.