chore: remove RST swap mechanism, archive rst-*.rst under docs/_rst_legacy/

The swap mechanism (RST-as-fallback for migrated MD pages) is dormant —
docs/_rst_overrides.txt has been empty since the MyST flip trio
landed. The mechanism's surface area is dead weight and the rst-*.rst
shadows scattered across the source tree cause Context7's parser to
misclassify the project as RST.

Sibling PRs:
- yuriy/remove-rst-swap-mechanism (rolling)
- yuriy/remove-rst-swap-mechanism-circinus

Changes:
- Move 210 rst-*.rst shadow files into docs/_rst_legacy/ preserving
  subdirectory structure. They remain in the repo for reference; Sphinx
  excludes the folder via exclude_patterns.
- Strip swap_sources.py invocation from docs/Makefile.
- Strip rst-*.rst exclude entry and the _md_exclude.txt loader from
  docs/conf.py; replace with a single _rst_legacy exclude.
- Delete scripts/swap_sources.py, tests/test_swap_sources.py,
  docs/_rst_overrides.txt.
- Update AGENTS.md: drop the "RST override mechanism" section and the
  test-runner snippet for the deleted test.

Note: .readthedocs.yml on sagitta has no jobs: block to remove (the
swap was wired only at build-time via the Makefile chain on this branch).

Verified: sphinx-build -b html with --keep-going produces identical
warning set (409 unique — pre-existing cli.rst/aws.rst title-level
warnings on this branch), identical sitemap entry count (215),
identical llms.txt entry count (23), zero rst-* URLs in any artifact.

🤖 Generated by [robots](https://vyos.io)

2 files changed, 0 insertions, 163 deletions

diff --git a/docs/introducing/rst-about.rst b/docs/introducing/rst-about.rst
deleted file mode 100644
index 944ff0a1..00000000
--- a/docs/introducing/rst-about.rst
+++ /dev/null
@@ -1,27 +0,0 @@
-.. _about:
-
-#####
-About
-#####
-
-VyOS is an open source network operating system based on Debian GNU/Linux.
-
-VyOS provides a free routing platform that competes directly with other
-commercially available solutions from well known network providers. Because
-VyOS runs on standard amd64, i586 and ARM systems, it is able to be used
-as a router and firewall platform for cloud deployments.
-
-We use multiple live versions of our manual, hosted thankfully by
-https://readthedocs.org. We will provide one version of the manual for every
-VyOS major version starting with VyOS 1.2 which will receive Long-term support
-(LTS).
-
-The manual version is selected/specified by it's Git branch name. You can
-switch between versions of the documentation by selecting the appropriate
-branch on the bottom left corner.
-
-VyOS CLI syntax may change between major (and sometimes minor) versions. Please
-always refer to the documentation matching your current, running installation.
-If a change in the CLI is required, VyOS will ship a so called migration script
-which will take care of adjusting the syntax. No action needs to be taken by
-you.
diff --git a/docs/introducing/rst-history.rst b/docs/introducing/rst-history.rst
deleted file mode 100644
index 40b99b02..00000000
--- a/docs/introducing/rst-history.rst
+++ /dev/null
@@ -1,136 +0,0 @@
-.. _history:
-
-#######
-History
-#######
-
-In the beginning...
-===================
-
-There once was a network operating system based on Debian GNU/Linux,
-called Vyatta. [*]_ 2006 onwards, it was a great free software
-alternative to Cisco IOS and Jupiter JUNOS. It came in two editions:
-Vyatta Core (previously Vyatta Community Edition) that was completely
-free software, and Vyatta Subscription Edition that had proprietary
-features and was only available to paying customers. [*]_
-
-Vyatta was acquired by Brocade Communication Systems in 2012. Shortly
-after, Brocade renamed Vyatta Subscription Edition to Brocade vRouter,
-discontinued Vyatta Core and shut down the community forum without a
-notice. The bug tracker and Git repositories followed next year.
-
-It's worth noting that by the time Brocade acquired Vyatta,
-development of Vyatta Core was already stagnated. Vyatta Subscription
-Edition (and thus, Vyatta development as a whole) had been replacing
-core components with proprietary software, meaning few features made
-it to Vyatta Core, and those that did were bug-ridden and hamstrung.
-
-In 2013, soon after Vyatta Core was abandoned, the community forked
-the last Vyatta Core version (6.6R1) and VyOS Project came into being.
-`Sentrium SL <https://blog.vyos.io/sentrium-what-sentrium>`_ was
-established by VyOS maintainers in 2014 to fund VyOS development by
-selling support, consulting services and prebuilt long-term support
-images.
-
-Brocade was acquired by Broadcom in 2016 and sold what remains of
-erstwhile Vyatta to AT&T in 2017, who in turn sold it to Ciena in 2021.
-
-
-Major releases
-==============
-
-VyOS major versions used to be named after elements in order of atomic
-numbers. With 1.2, this naming scheme was replaced with the much
-cooler scheme of Latin names of `IAU
-<https://en.wikipedia.org/wiki/IAU_designated_constellations_by_area>`_
-designated constellations by solid angle area, starting from the smallest.
-
-Hydrogen (1.0)
---------------
-
-Released just in time for holidays on 22 December 2013, Hydrogen was
-the first major VyOS release. It fixed features that were broken in
-Vyatta Core 6.6 (such as IPv4 BGP peer groups and DHCPv6 relay) and
-introduced command scripting, a task scheduler and web proxy LDAP
-authentication.
-
-Helium (1.1)
-------------
-
-Helium was released on 9 October 2014, exactly on the day VyOS Project
-first came into being in the previous year. Helium came with a lot of
-new features, including an event handler and support for L2TPv3,
-802.1ad QinQ and IGMP proxy, as well as experimental support for VXLAN
-and DMVPN (the latter of which was also broken in Vyatta Core due to
-its reliance on a proprietary NHRP implementation).
-
-Crux (1.2)
-----------
-
-Crux (the Southern Cross) came out on 28 January 2019 and was the
-first major release of VyOS as we know it today. The underlying
-Debian base was upgraded from Squeeze (6) to Jessie (8).
-
-Although Crux came with too many new features to mention here, some
-noteworthy ones are: an mDNS repeater, a broadcast relay,
-a high-performance PPPoE server, an HFSC scheduler, as well as support
-for Wireguard, unicast VRRP, RPKI for BGP and fully 802.1ad-compliant
-QinQ ethertype. The telnet server and support for P2P filtering were
-removed.
-
-Crux is the first version to feature the modular image build system.
-CLI definitions began to be written in the modern, verifiable XML
-templates. Python APIs were introduced for command scripting and
-configuration migration. Introduction of new Perl and shell code was
-proscribed and the rewriting of legacy Perl code in pure Python began
-with Crux.
-
-As of 2022, Crux is still supported and maintained.
-
-Equuleus (1.3)
---------------
-
-The current long-term support version of VyOS, Equuleus (the Pony)
-came out on 21 December 2021, once again in time for the winter
-holidays.
-
-Equuleus brought many long-desired features with it, most notably
-an SSTP VPN server, an IPoE server, an OpenConnect VPN server and
-a serial console server, in addition to reworked support for WWAN
-interfaces, support for GENEVE and MACSec interfaces, VRF, IS-IS
-routing, preliminary support for MPLS and LDP, and many other
-initialisms.
-
-As of 2022, Equuleus is in the stable.
-
-Sagitta (1.4)
--------------
-
-Sagitta (the Arrow) is the codename of the current development
-branch, so there's no VyOS 1.4 yet.
-
-Circinus (1.5)
---------------
-
-Circinus (the Compass) is the codename of the upcoming development
-branch, so there's no VyOS 1.5 yet.
-
-A note on copyright
-===================
-
-Unlike Vyatta, VyOS never had (nor will ever have) proprietary code.
-The only proprietary material in VyOS is non-code assets, such as
-graphics and the trademark "VyOS". [*]_ This means you can build your
-own long-term support images (as the entire toolchain we use is free
-software) and even distribute them, given you rename it and remove
-such assets before building. Although note that we do not provide
-support for images distributed by a third-party. See the
-`artwork license <https://github.com/vyos/vyos-build/blob/current/LICENSE.artwork>`_
-and the end-user license agreement at ``/usr/share/vyos/EULA`` in
-any pre-built image for more precise information.
-
-
-.. [*] From the Sanskrit adjective "Vyātta" (व्यात्त), meaning opened.
-.. [*] A business model comparable to that of Redis, rather than that
-       of VyOS today.
-.. [*] This is not unlike how Linus Torvalds owns the trademark "Linux".