Use the build's own hash file, not shasum, which Windows does not have

With the Windows tests, build, smoke and npm-pack checks all green, the last
red on that platform was a step I wrote: `shasum -a 256`, a Unix tool.

build.mjs already writes dist/seedpass-js.mjs.sha256 over exactly the file
users execute, so the workflow reads that instead of computing it again with
whatever happens to be installed. Fewer assumptions and one fewer thing that
can differ per platform — which is the entire point of this workflow.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01Vtx94nXDmNgXEeThUZP4QN

.github/workflows/ts-platform.yml

@@ -84,8 +84,12 @@ jobs:
           npm install "$TARBALL" > /dev/null
           ./node_modules/.bin/seedpass-js --version
       - name: Record the bundle hash
+        # build.mjs already writes dist/seedpass-js.mjs.sha256 over exactly
+        # the file users execute, so use that rather than reaching for
+        # `shasum` -- which does not exist on Windows, and was the last thing
+        # failing there after the tests themselves went green.
         run: |
-          shasum -a 256 packages/cli/dist/seedpass-js.mjs | awk '{print $1}' \
+          cut -d' ' -f1 packages/cli/dist/seedpass-js.mjs.sha256 \
             > "$RUNNER_TEMP/bundle.sha256"
           echo "${{ matrix.os }}: $(cat "$RUNNER_TEMP/bundle.sha256")"
       - uses: actions/upload-artifact@v4