fix(install,studio): address Codex round-4 review (6 of 7 comments real)

- install.sh: gate the new aarch64 bitsandbytes block on SKIP_TORCH=false --
  with --no-torch/UNSLOTH_NO_TORCH (GGUF-only install) it would have pulled
  torch back into the venv through bitsandbytes' dependencies.

- studio worker: in the new Spark OOM-guard section, decide
  PYTORCH_CUDA_ALLOC_CONF (expandable_segments) BEFORE the guard's first CUDA
  touch -- get_device_properties initializes the CUDA allocator, after which
  the env var is ignored, and the later `import unsloth`
  (patch_dgx_spark_memory_config) is too late for the worker process. Uses
  the same CUDA-free nvidia-smi name sniff, append-don't-override, and
  UNSLOTH_NO_EXPANDABLE_SEGMENTS opt-out as the library patch. Live-verified
  on the N1X: env set while torch.cuda.is_initialized() is still False.

- uninstall.ps1: only run `fuser -k 8888/tcp` in a probed WSL distro when an
  Unsloth install actually exists there (checked BEFORE the rm deletes the
  marker) -- an unrelated listener on 8888 (e.g. Jupyter) in a clean distro
  must survive a Windows-side uninstall. The Unsloth-specific pkills stay
  unconditional.

- install.ps1 + uninstall.ps1: persist the chosen WSL distro to
  %LOCALAPPDATA%\Unsloth\wsl-distro.txt at install; uninstall reads it
  (before removing the directory) and prepends it to the cleanup candidates,
  so a custom UNSLOTH_WSL_DISTRO install is cleaned without the env var
  being set again at uninstall time.

- provision_llama_cuda.sh: honor UNSLOTH_LLAMA_PR (numeric-validated,
  best-effort fetch of pull/N/head after clone) so a provisioned tree
  matches a PR pin the way setup.sh does; and require only llama-server in
  the main cmake build (mirroring setup.sh), building the helper targets
  (llama-cli/quantize/mtmd-cli/gguf-split) best-effort afterwards -- an
  older UNSLOTH_LLAMA_TAG pin lacking a newer helper target no longer fails
  the whole provision.

Not changed: the "--tauri rejection doesn't restore the venv rollback"
comment is incorrect -- the rejection returns through Exit-InstallFailure,
which itself calls Restore-StudioVenvRollback.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/uninstall.ps1

@@ -344,6 +344,19 @@ function Uninstall-UnslothStudio {
     # %LOCALAPPDATA%\Unsloth (not "Unsloth Studio") with a PATH entry -- all missed by the cleanup above.
     _Step "Removing WSL-fallback artifacts (shim, launcher, PATH entry, WSL install)..."
     $unslothDir = if ($env:LOCALAPPDATA) { Join-Path $env:LOCALAPPDATA "Unsloth" } else { $null }
+    # The installer records its WSL distro in wsl-distro.txt so a custom
+    # UNSLOTH_WSL_DISTRO install is cleanable without the env var being set again
+    # at uninstall time. Read it BEFORE the directory is removed below.
+    $_recordedDistro = $null
+    if ($unslothDir) {
+        try {
+            $_distroFile = Join-Path $unslothDir "wsl-distro.txt"
+            if (Test-Path -LiteralPath $_distroFile) {
+                $_recordedDistro = (Get-Content -LiteralPath $_distroFile -ErrorAction SilentlyContinue | Select-Object -First 1)
+                if ($_recordedDistro) { $_recordedDistro = $_recordedDistro.Trim() }
+            }
+        } catch { }
+    }
     if ($unslothDir) {
         $shimDir = (Join-Path $unslothDir "bin").TrimEnd('\', '/')
         try {
@@ -379,8 +392,13 @@ function Uninstall-UnslothStudio {
             # touching /home/*/.unsloth would erase an unrelated WSL user's own Unsloth/cache that this
             # installer never created. pkill patterns use the [x]-regex self-exclusion trick: '[u]nsloth_studio'
             # keeps the shell's own argv from matching while real processes still match. Same for '[l]lama-server'.
-            $_clean = 'rm -rf /root/.unsloth /root/llama-cuda /root/provision_llama_cuda.sh /root/llama_cuda_build.log 2>/dev/null; rm -f /root/.local/bin/unsloth 2>/dev/null; fuser -k 8888/tcp 2>/dev/null; pkill -9 -f ''[u]nsloth_studio'' 2>/dev/null; pkill -9 -f ''[l]lama-server'' 2>/dev/null; true'
+            # The port-8888 kill is gated on an Unsloth install actually existing in the
+            # distro (checked BEFORE the rm deletes the marker): a probed distro with an
+            # unrelated listener on 8888 (Jupyter etc.) must not lose it. The pkills are
+            # already Unsloth-specific, so they stay unconditional.
+            $_clean = '_had=0; if [ -d /root/.unsloth ] || [ -L /root/.local/bin/unsloth ]; then _had=1; fi; rm -rf /root/.unsloth /root/llama-cuda /root/provision_llama_cuda.sh /root/llama_cuda_build.log 2>/dev/null; rm -f /root/.local/bin/unsloth 2>/dev/null; if [ $_had -eq 1 ]; then fuser -k 8888/tcp 2>/dev/null; fi; pkill -9 -f ''[u]nsloth_studio'' 2>/dev/null; pkill -9 -f ''[l]lama-server'' 2>/dev/null; true'
             $_cands = @('', 'Ubuntu', 'Ubuntu-24.04', 'Ubuntu-22.04', 'Debian')
+            if ($_recordedDistro) { $_cands = @($_recordedDistro) + $_cands }
             if ($env:UNSLOTH_WSL_DISTRO) { $_cands = @($env:UNSLOTH_WSL_DISTRO) + $_cands }
             $_done = @{}
             foreach ($d in $_cands) {