Publish immutable short firmware download links

Mirror pinned GitHub release bytes at shorter version-specific Pages URLs. Verify size, SHA-256 and firmware format before publishing, and preserve deployed alias identities across later site builds.

Add RAK4631 Full Companion 1.17.1.10 preview2 UF2 and native DFU ZIP aliases, a short-download directory, documentation and CI regressions. Existing flashing tools use the ZIP URL without losing board-family checks.

Validation: 16 short-link and Pages guard regressions, hosted-doc routing tests, firmware picker tests, full MkDocs build and exact UF2/ZIP byte checks.

docs/d.md

@@ -0,0 +1,35 @@
+<!-- meshcore-hosted-doc-link:start -->
+<p class="meshcore-hosted-doc-link"><a href="https://mikecarper.github.io/MeshCore/d/">View this page on MeshCore Docs</a>.</p>
+<!-- meshcore-hosted-doc-link:end -->
+
+# Short firmware links
+
+These links download the same firmware bytes as the original GitHub release,
+with shorter filenames. Each link is pinned to one version and verified against
+its SHA-256 checksum when the site is built. Existing links keep their original
+firmware; a new release gets a new link.
+
+<!-- firmware-shortlinks:table -->
+
+For **RAK4631 Full Companion**, use the **UF2** for a bootloader-drive
+drag-and-drop update. Use the **DFU ZIP** when pasting a custom download URL
+into the Windows or Linux MeshCore firmware tool. The ZIP is the native
+application update package, not the release's download bundle. These files do
+not install a bootloader or SoftDevice.
+
+The 1.17.1.10 preview2 files are for MeshTalk testing with Keymind Cascade and
+USA Cascade defaults. The original release includes instructions, qualification
+reports and checksums. See the [firmware picker](firmware_picker.md) for other
+board and release choices.
+
+## Adding links for another release
+
+Add an entry to `docs/_data/firmware_shortlinks.json` with a unique,
+version-specific filename, exact release tag and asset name, byte size, label
+and SHA-256 checksum from the validated release. Keep the original firmware
+extension. Never change or remove a published filename's version, source or
+checksum. Labels can be corrected without changing the download.
+
+The documentation build downloads and verifies the pinned files before
+publishing them under `d/`. A missing asset, incorrect checksum or changed
+published link stops deployment instead of publishing a different image.