Public export snapshot from bran-dev cd396e1 (Windows release packaging fix)

[1wgrumph]

Public export snapshot produced by the approved exporter from a clean committed source.

Source commit	cd396e16a2f4c9a53d95cab6eb2ef2d617964351
BRAN version	0.1.0
Public export commit	86e5ccd
Files	125

What this fixes

The first bran-v0.1.0 release run built successfully on Linux x86_64, Linux arm64, and macOS arm64, but failed on Windows while writing the archive:

FAIL failed to write ...\dist\bran-v0.1.0-x86_64-pc-windows-msvc.zip: Access is denied. (os error 5)

write_zip passed a File::create handle to write_zip_to, which calls patch_zip_external_attr to read the end-of-central-directory record back. File::create opens write-only, so the read failed at runtime. It compiled because File implements Read.

The zip branch only executes for the Windows target, and every existing zip test passed io::Cursor, which is always readable — so the path-taking entry point the release actually calls had never been exercised on any platform.

Added a regression test that writes a real file and reads it back. It reproduces the failure on Linux (os error 9, bad file descriptor) without the fix, so this is covered off-Windows from now on.

Validation

publish-hygiene PASS — files=248
PASS public snapshot / drift guard: source_commit=cd396e1... files=125
cargo test: 43 bran-cli, 279 bran-core, 5 xtask — 0 failed
PASS Phase 1 through Slice 3.4 fast gate   (exit 0)
tar.gz packaging verified byte-deterministic across two runs

Rebase-merge, not squash.