fix: no-torch install deps without pulling torch transitively (#4650)

Use --no-deps for ALL packages (unsloth, unsloth-zoo, and runtime deps)
since the current PyPI metadata for unsloth still declares torch as a
hard dependency. Runtime deps (typer, pydantic, safetensors,
transformers, etc.) are installed from no-torch-runtime.txt with
--no-deps to prevent transitive torch resolution from accelerate, peft,
trl, and sentence-transformers.

no-torch-runtime.txt now includes unsloth's own direct deps (typer,
pydantic, pyyaml, nest-asyncio) since --no-deps skips those too.

install.sh installs no-torch-runtime.txt directly (via helper function
_find_no_torch_runtime). install.ps1 does the same via
Find-NoTorchRuntimeFile. SKIP_STUDIO_BASE stays at 1 to avoid setup.sh
fast-path issues.

install_python_stack.py NO_TORCH branch does the same for unsloth
studio update, using package_name instead of hardcoded "unsloth".

studio/install_python_stack.py

@@ -462,13 +462,25 @@ def install_python_stack() -> int:
     if skip_base:
         print(_green(f"✅ {package_name} already installed — skipping base packages"))
     elif NO_TORCH:
-        # No-torch mode: unsloth + unsloth-zoo are already installed with
-        # --no-deps by install.sh/install.ps1. Install the runtime deps
-        # (safetensors, transformers, datasets, etc.) from no-torch-runtime.txt.
+        # No-torch update path: install unsloth + unsloth-zoo with --no-deps
+        # (current PyPI metadata still declares torch as a hard dep), then
+        # runtime deps with --no-deps (avoids transitive torch).
         _progress("base packages (no torch)")
+        pip_install(
+            f"Updating {package_name} + unsloth-zoo (no-torch mode)",
+            "--no-cache-dir",
+            "--no-deps",
+            "--upgrade-package",
+            package_name,
+            "--upgrade-package",
+            "unsloth-zoo",
+            package_name,
+            "unsloth-zoo",
+        )
         pip_install(
             "Installing no-torch runtime deps",
             "--no-cache-dir",
+            "--no-deps",
             req = REQ_ROOT / "no-torch-runtime.txt",
         )
         if local_repo: