Add a Repositories and mirrors page to the OpenVox 8.x and 9.x docs

[miharp]

Adds a "Repositories and mirrors" page to the OpenVox 8.x and 9.x collections, placed after "OpenVox repositories and packages" in the Installing and upgrading section, and links it from the Linux install page and the repositories page in both series.

Part of #479. Part of #442 (the "Managing OpenVox with OpenVox" repository snippets now live here instead of the microsite).

What the page covers

• Canonical URLs and layout: the five voxpupuli.org names, the rsync.voxpupuli.org tree they map onto, the apt suite/component and yum path conventions, and the signing key (one key for everything, fingerprint 0E26 4299 8700 2418 F951 3F2A 5FB9 99C2 D62F F3D9, published as GPG-KEY-openvox.pub and openvox-keyring.gpg). Notes that *.overlookinfratech.com and s3.osuosl.org/openvox-* are the same server, not mirrors.
• Public mirror table: seven mirrors from Set up mirrors page on voxpupuli.org planning#41 with location, protocols, contents, and sync interval, plus a dated "last checked" note and a warning that the project does not monitor them.
• Using a mirror: a .repo file, an apt keyring + sources + preferences set, and yumrepo / apt::source / apt::pin equivalents. Setting $mirror to https://rsync.voxpupuli.org makes the same code use the canonical repositories.
• Running your own mirror: both rsync modules with measured sizes, a sample rsync command, and how to get listed.

The 8.x and 9.x copies differ only in the series string (openvox8/openvox9).

Also in this PR

The 9.x install_linux and openvox_platform pages still told readers to install openvox8-release. Fixed to openvox9-release since both pages were being edited anyway.

Verification (2026-09-10)

• Every mirror in the table serves yum/openvox9-release-el-9.noarch.rpm over https and carries the signing key files. Rackspace has no artifacts/; nfrance has only apt/ and yum/; both are marked in the Contents column.
• Release package contents (yum baseurl, apt sources line, apt preference) were taken from the actual openvox9-release-el-9.noarch.rpm and openvox9-release-ubuntu24.04.deb, not from memory.
• The .repo and apt examples were run as written in almalinux:9 and ubuntu:24.04 containers against mirror.rackspace.com: dnf install --downloadonly openvox-agent imports the key from the mirror and downloads the package; apt-cache policy shows the 1001 pin and apt-get install --download-only succeeds.
• Repository sizes come from rsync -rn --stats against both modules (packages ≈ 97 GB in 4,190 files; all ≈ 497 GB in 37,747 files).
• jekyll build clean, markdownlint-cli2 clean on all six touched files, in-page links resolve in _site for 8.x, 9.x, and latest.

Mirrors not listed

• mirror.its.dal.ca (Canada): unreachable on 2026-09-10, so left out until it is confirmed back.
• mirror.aarnet.edu.au (Australia): offered in planning#41 but never went live (404).

Things for reviewers to decide

• linorg.usp.br (Brazil) was about five weeks behind when checked: newest packages were openvox-agent-8.28.1 and 9.0.0~beta1, so it is missing 8.29.0 and 9.0.0-rc1 despite the stated daily sync. It is in the table because it is reachable and the operator advertises daily syncs, but it may be better to drop it or contact linorg@usp.br first.
• Recommendation: the page tells readers to pick the nearest mirror and says Rackspace's geo-DNS makes it "a reasonable choice for nodes spread across several regions". That is as close to a recommendation as I went; happy to make it stronger or remove it.
• Fastly (planning#50) is not mentioned. If the CDN lands, the mirror section becomes optional reading and the page should say so then.
• Liveness check: not included. A scheduled workflow that HEADs one file per mirror (and ideally compares the newest package name against origin, since reachability alone missed the Brazil staleness) would keep the table from rotting. Can be a follow-up issue.
• planning#41 still needs a comment pointing at the page once it is live (last checkbox in Document OpenVox repository URLs and public mirrors #479); not done from this PR.

Assisted by Claude.