fix(test): first cross-platform run of the wave's tests — Linux tmp portability + Windows-lane truthfulness

Four platform holes from the lanes' first full run over the v1.67 tests:

- uninstall neutral-root fallback hardcoded /private/tmp (macOS-only) and
  ENOENT'd on Linux CI, where the shard TMPDIR is the gstack-containing
  path that forces the fallback — now realpath'd literal /tmp.
- uninstall's kept-and-listed assertion demanded a backslash path on
  Windows while the bash uninstall prints POSIX paths — now
  separator-insensitive.
- setup-rerun's IS_WINDOWS=0 sub-case and the iron rule's force-restart
  consent path are Unix-shaped by construction (Git Bash ln -snf copies
  without Developer Mode; the consent path boots a real replacement daemon
  the browserless Windows lane cannot host) — gated off win32 with the
  reasons in place; the Windows-relevant halves still run there.
- codex-under-codex-detection drives rendered bash under a hardcoded POSIX
  PATH, so every case saw empty output on Windows — moved to
  KNOWN_WINDOWS_INCOMPATIBLE with the run receipt.

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

test/setup-windows-rerun-refresh.test.ts

@@ -274,6 +274,11 @@ describe('setup: Windows re-run refresh — behavior fixture (#2444)', () => {
     // On Unix the asset is a SYMLINK into the working tree; pruning through
     // it would delete real build output from the repo. The prune is gated on
     // the Windows real-copy shape ([ -d ] && [ ! -L ]).
+    // Not runnable ON Windows: this sub-case models the UNIX shape, but Git
+    // Bash's `ln -snf` produces a real copy there (no Developer Mode on CI),
+    // so the symlink assertion is false by platform, not by regression. The
+    // Unix lanes (macOS dev boxes + Linux CI) own this case.
+    if (process.platform === 'win32') return;
     const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-rerun-prune-unix-'));
     try {
       const src = path.join(tmp, 'skill-src');