feat: flip swap mechanism — MD as primary, RST as override (Phase 1)

This is the first of three phases inverting the per-page swap mechanism
so MD becomes the canonical primary and RST becomes the rare override.

Phase 1 — file renames + conf.py exclude_patterns flip only:
- Rename docs/**/md-<stem>.md to docs/**/<stem>.md (drop md- prefix)
  for all 254 stems previously listed in docs/_swap.txt
- Rename docs/**/<stem>.rst to docs/**/rst-<stem>.rst (add rst- prefix)
  for the same 254 stems
- Repurpose docs/_swap.txt as docs/_rst_overrides.txt; initially empty
  comment-only since no pages need the RST fallback right now
- conf.py exclude_patterns flipped: rst-*.rst is now excluded by default
  instead of md-*.md
- conf.py runtime-artifact references updated to _rst_override_state.json
  and _md_exclude.txt (Phase 2 will rewrite swap_sources.py to produce
  these names; for now no swap script runs because overrides list is empty)

Phase 2 (next commit on this branch) will rewrite scripts/swap_sources.py
with inverted rename direction, delete scripts/import_myst.py + tests, and
update tests/test_swap_sources.py for the new semantics.

Phase 3 will be the cleanup pass and ready-for-review flip.

Generated by robots https://vyos.io

1 files changed, 36 insertions, 0 deletions

diff --git a/docs/configuration/system/updates.md b/docs/configuration/system/updates.md
new file mode 100644
index 00000000..c82d37be
--- /dev/null
+++ b/docs/configuration/system/updates.md
@@ -0,0 +1,36 @@
+# Updates
+
+VyOS supports online checking for updates
+
+## Configuration
+
+```{cfgcmd} set system update-check auto-check
+
+Configure auto-checking for new images
+```
+
+```{cfgcmd} set system update-check url \<url\>
+
+Configure a URL that contains information about images.
+```
+
+
+## Example
+
+```none
+set system update-check auto-check
+set system update-check url 'https://raw.githubusercontent.com/vyos/vyos-rolling-nightly-builds/main/version.json'
+```
+
+Check:
+
+```none
+vyos@r4:~$ show system updates
+Current version: 1.5-rolling-202312220023
+
+Update available: 1.5-rolling-202312250024
+Update URL: https://github.com/vyos/vyos-rolling-nightly-builds/releases/download/1.5-rolling-202312250024/1.5-rolling-202312250024-amd64.iso
+vyos@r4:~$
+
+vyos@r4:~$ add system image latest
+```