v1.2.26-open-runtime-fork.2

feat(release): add Windows ARM64 binary to release matrix

- Add windows-11-arm runner to build matrix for windows/arm64
- Add windows-arm64 row to release download table
- Fix packaging step conditionals to use matrix.platform instead of
  matrix.os so both Windows runners (windows-latest, windows-11-arm)
  correctly use PowerShell Compress-Archive

The build script (build.ts) already supports win32/arm64 in
allTargets — this just adds the CI runner to actually build it.
Bun has supported Windows ARM64 natively since v1.3.10.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>