fix(setup): BROWSE_BIN carries the .exe suffix on Windows

On Windows, `bun build --compile` emits browse.exe, but setup's
BROWSE_BIN pointed at the suffixless path — so the post-build gate
(`[ ! -x "$BROWSE_BIN" ]` → "browse binary missing") could never pass on
Windows even after a fully successful build, while the build step itself
reported success. Closes #2291.

Applied the PR's override after the IS_WINDOWS detection, and also to
the second BROWSE_BIN assignment the PR predates: the direct-Codex-
install migration path re-derives BROWSE_BIN from the migrated dir and
would otherwise drop the suffix again on Windows.

Contributed by @rroojrooj (PR #1714).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

setup

@@ -30,6 +30,11 @@ case "$(uname -s)" in
   MINGW*|MSYS*|CYGWIN*|Windows_NT) IS_WINDOWS=1 ;;
 esac
 
+# Windows: binaries are compiled with .exe suffix
+if [ "$IS_WINDOWS" -eq 1 ]; then
+  BROWSE_BIN="$SOURCE_GSTACK_DIR/browse/dist/browse.exe"
+fi
+
 # ─── Symlink-or-copy helper ───────────────────────────────────
 # On macOS/Linux: create a symlink (existing behavior).
 # On Windows without Developer Mode (MSYS2/Git Bash): plain ln -snf silently
@@ -243,6 +248,11 @@ migrate_direct_codex_install() {
   INSTALL_GSTACK_DIR="$migrated_dir"
   INSTALL_SKILLS_DIR="$(dirname "$INSTALL_GSTACK_DIR")"
   BROWSE_BIN="$SOURCE_GSTACK_DIR/browse/dist/browse"
+  # Windows: binaries are compiled with .exe suffix (same as the top-level
+  # BROWSE_BIN assignment — this re-derivation must not drop the suffix).
+  if [ "$IS_WINDOWS" -eq 1 ]; then
+    BROWSE_BIN="$SOURCE_GSTACK_DIR/browse/dist/browse.exe"
+  fi
 }
 
 if [ "$INSTALL_CODEX" -eq 1 ]; then