ci(release): build windows-arm64 desktop as a portable zip only

The windows-11-arm leg added by the previous commit runs
`packageReleaseMsi`, which cannot succeed on that runner: jpackage
--type msi shells out to WiX 3's heat.exe / candle.exe / light.exe
(JDK 21 jpackage guide names WiX 3.11.1), and the Windows 11 Arm64
runner image ships no WiX at all.

Verified against actions/runner-images:
  images/windows/Windows2025-Readme.md    -> "WiX Toolset 3.14.1.8722"
  images/windows/Windows11-Arm64-Readme.md -> no WiX entry
(7zip 26.02, Python 3.13 and Java 21 aarch64 ARE present on the arm64
image, so the rest of the leg — createReleaseDistributable, the 7z
portable zip, collect_assets — is unaffected.)

Installing WiX in the job instead was the alternative and is worse:
wixtoolset/wix3 was archived in Feb 2025, WiX 4+ replaced the
candle/light CLI that jpackage drives with `wix build`, and the WiX 3
binaries are x86-only (emulated on arm64). That would mean pulling an
archived, unpinned third-party toolchain into the job that publishes
signed release assets, for one asset we already ship in portable form.

So: arm64 Windows gets the portable .zip, which is already the
documented Windows install path for amy and geode. The x64 leg is
untouched and still produces the MSI.

collect_assets needs no change — it globs with nullglob and skips the
absent msi/ directory.

BUILDING.md: replace the release-verification asset count, which this
branch had left vague ("5 formats x 2 arches shipped as one merged set
of 5 ... see the previous release"), with a per-leg enumeration counted
off the matrix: 14 desktop + 13 Android + 10 amy + 10 geode = 47. Also
corrects the Windows prerequisites note, which claimed CI produces
arm64 MSIs natively.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.github/workflows/create-release.yml

@@ -48,10 +48,22 @@ jobs:
         # public-repo runner catalogue in 2025 (4 vCPU / 16 GB / arm64).
         # jpackage / jlink / Compose Multiplatform 1.11 all produce
         # host-native artifacts — no cross-compilation needed.
+        #
+        # The arm64 Windows leg builds the portable .zip ONLY — no MSI.
+        # jpackage --type msi shells out to WiX 3's heat/candle/light, and the
+        # windows-11-arm runner image ships no WiX (the windows-latest image
+        # has WiX 3.14 preinstalled, which is why the x64 leg can package an
+        # MSI). Installing it here would mean pulling an archived, x86-only
+        # toolchain (wixtoolset/wix3 was archived in Feb 2025; WiX 4+ dropped
+        # the candle/light CLI that JDK 21's jpackage requires) into the job
+        # that publishes signed release assets. The portable zip is the
+        # documented Windows install path for amy/geode already, so arm64
+        # Windows users get that until either the runner image gains WiX or
+        # jpackage learns the WiX 4+ CLI.
         include:
           - { os: macos-14,         arch: arm64, family: macos,          tasks: "packageReleaseDmg" }
           - { os: windows-latest,   arch: x64,   family: windows,        tasks: "packageReleaseMsi createReleaseDistributable" }
-          - { os: windows-11-arm,   arch: arm64, family: windows,        tasks: "packageReleaseMsi createReleaseDistributable" }
+          - { os: windows-11-arm,   arch: arm64, family: windows,        tasks: "createReleaseDistributable" }
           - { os: ubuntu-latest,    arch: x64,   family: linux,          tasks: "packageReleaseDeb packageReleaseRpm" }
           - { os: ubuntu-24.04-arm, arch: arm64, family: linux,          tasks: "packageReleaseDeb packageReleaseRpm" }
           - { os: ubuntu-latest,    arch: x64,   family: linux-portable, tasks: "createReleaseAppImage createReleaseDistributable" }