docs(packaging): add the 2.2.0 release entry

CI takes the newest <release> as the notes of a tag and refuses a tag
that does not match it. 2.2.0 covers what changed since 2.1.0: Shader
entries with per-entry defines and a named output variant, sysroot
compiles against the sysroot's own libc++ headers, a project.so stamp
that hashes every part of the host build, and the vendored json.hpp
removed.

The variant API is what catcrafts.net's deploy needs: Crafter.Graphics
master has used it since 2026-10-06, and a stable Flatpak that lacks it
cannot build the site.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

packaging/flatpak/net.catcrafts.CrafterBuild.metainfo.xml

@@ -25,6 +25,12 @@
   </provides>
   <content_rating type="oars-1.1"/>
   <releases>
+    <release version="2.2.0" date="2026-10-16">
+      <description>
+        <p>A Shader entry can carry defines, spelled like the compiler's -D (NAME is defined to 1, NAME=VALUE to VALUE), and a variant that names its output, so one source compiles into several outputs: ui.comp.glsl with variant sets becomes ui.comp.sets.spv. A configuration in which two entries share an output name is refused with both named, as are a malformed define and a variant with a path separator.</p>
+        <p>Compiles with a sysroot now use the sysroot's own libc++ headers instead of the bundled toolchain's, which fixes cross builds against a musl sysroot that include a standard header textually and stops glibc sysroot builds from silently compiling against the wrong libc++ release. The project.so stamp hashes every part of the host build, so a changed declaration recompiles it. The vendored json.hpp is gone.</p>
+      </description>
+    </release>
     <release version="2.1.0" date="2026-10-03">
       <description>
         <p>The bundled toolchain is now LLVM 23.1.2. Build outputs are kept per compiler, so the first build after updating recompiles each project into a fresh directory and nothing has to be cleaned by hand.</p>