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, 21 insertions, 0 deletions

diff --git a/docs/introducing/about.md b/docs/introducing/about.md
new file mode 100644
index 00000000..ec4ff30d
--- /dev/null
+++ b/docs/introducing/about.md
@@ -0,0 +1,21 @@
+(about)=
+
+# About
+
+VyOS is an open-source network operating system that provides a single unified
+CLI and API to manage routing protocols, firewall and NAT, QoS, load balancing,
+DHCP and DNS servers, and many other features.
+
+VyOS runs on a wide variety of commodity hardware, virtual machines, and
+multiple cloud environments.
+
+We provide a dedicated user guide for each major
+VyOS release that receives long-term support (LTS). We maintain multiple user
+guide versions, all hosted at <https://docs.vyos.io>.
+To switch between versions, select the appropriate version in the bottom-right
+corner.
+
+VyOS CLI syntax may vary between major and sometimes minor releases. Always
+refer to the documentation matching your current running installation. If
+a change in the CLI is required, VyOS provides a migration script to handle
+the syntax adjustments. No user action is required.