R6.11 round 1 fix: the installer removes only what it installed

Reinstalling deleted files Ely never installed, and a busy file left a
half-removed install. The installer now writes the top-level names it
installs (.ely-files, from packaging/windows/files.sh); upgrades and
uninstall remove only those, and releases before the list only in the
folder the registry names. It checks that every listed file can be
written, moves them all into .ely-old, and on any refusal puts them
back and exits 2. A file that cannot be written fails the install,
which removes what it created and restores the old release.
tests/scripts/windows-installer.sh covers each case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packaging/windows/installer.sh

@@ -20,10 +20,12 @@ stage=$root/target/stage/$slug
 "$root/packaging/stage.sh" "$slug" "$stage"
 types=$root/target/stage/$slug-types.nsh
 "$root/packaging/windows/types.sh" "$slug" >"$types"
+files=$root/target/stage/$slug-files.nsh
+"$root/packaging/windows/files.sh" "$stage" "$slug" >"$files"
 mkdir -p "$dist"
 out=$dist/$name-$version-windows-x86_64-setup.exe
 "$makensis" -V2 -INPUTCHARSET UTF8 -DAPP_NAME="$name" -DAPP_SLUG="$slug" -DVERSION="$version" \
   -DSTAGE="$(cygpath -w "$stage")" -DICON="$(cygpath -w "$root/assets/icons/$slug.ico")" \
-  -DTYPES="$(cygpath -w "$types")" -DOUTFILE="$(cygpath -w "$out")" \
+  -DTYPES="$(cygpath -w "$types")" -DFILES="$(cygpath -w "$files")" -DOUTFILE="$(cygpath -w "$out")" \
   "$(cygpath -w "$root/packaging/windows/installer.nsi")"
 echo "$out"