* fix(bundles): write the build stamp before flavored icons land
A flavored build (commit, canary, preview channel) copies its icons over the
committed apps/desktop/assets before packaging. write-build-stamp ran after
that copy, so its git check saw modified tracked files and stamped the
bundle dirty, and the Windows smoke refused it (stamp.dirty: true != false),
which keeps a channel from promoting the build. Stamp first, in both the CI
driver (scripts/bundles/desktop.py) and the source build (build.mjs). The
stamp reads no artwork, so its content is unchanged.
* test(bundles): pin the build stamp ahead of the flavored icon copy
buildSourceDesktop copies flavored icons over committed files in
apps/desktop/assets. write-build-stamp asks git whether tracked files
changed, so it has to run while the committed bytes are still there. The
test records what the stamp step sees through the injectable run seam.
It fails on the old order (sees the flavored icon) and passes on the new one.
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