fix(studio/rocm): OOM guard ROCm-only + unified memory, multi-GPU arch selection

OOM guard (worker.py):
- Scope to _hw.IS_ROCM only -- NVIDIA CUDA has a graceful OOM path and
  does not need the allocator cap
- Detect unified memory by comparing torch VRAM against psutil system RAM;
  use 0.80 on unified-memory APUs (gfx1151 Strix Halo) where the GPU pool
  is carved from host RAM, 0.90 on discrete cards

Multi-GPU arch selection:
- install.ps1 / setup.ps1: replace -match (first hit only) with
  [regex]::Matches() to collect all gcnArchName entries, then index by
  HIP_VISIBLE_DEVICES / ROCR_VISIBLE_DEVICES
- install_python_stack.py: index into full token list before dedup so
  HIP_VISIBLE_DEVICES=2 on [gfx1100, gfx1100, gfx1151] resolves gfx1151
- install.sh: remove awk dedup from gfx token collection for same reason

GCC multiarch (setup.sh):
- Only append -linux-gnu when gcc -print-multiarch does not already return
  the full triple, fixing double-suffix on Ubuntu 24.04

studio/install_python_stack.py

@@ -271,11 +271,9 @@ def _detect_windows_gfx_arch() -> str | None:
     def _dedup_pick(tokens: list[str]) -> "str | None":
         if not tokens:
             return None
-        _seen: list[str] = []
-        for _t in tokens:
-            if _t not in _seen:
-                _seen.append(_t)
-        return _seen[_pick_visible_index(len(_seen))]
+        # Index into the full (ordered) list first so HIP_VISIBLE_DEVICES
+        # correctly addresses GPU N on mixed-arch hosts, then return that arch.
+        return tokens[_pick_visible_index(len(tokens))]
 
     # 2. hipinfo via PATH, then HIP_PATH\bin / ROCM_PATH\bin.
     hipinfo = shutil.which("hipinfo")