Add a POSIX sysconf fallback for local RAM detection

Retain the unsuperseded macOS RAM-detection contribution from PR #13 while making every optional probe fail closed. The shared MPS device, loader, cache, and dtype work is already present on current main and is intentionally not duplicated.

obliteratus/local_ui.py

@@ -100,16 +100,27 @@ def _get_ram_gb() -> float:
         import psutil
 
         return round(psutil.virtual_memory().total / 1024**3, 1)
-    except ImportError:
-        # Fallback: read from /proc/meminfo on Linux
-        try:
-            with open("/proc/meminfo") as f:
-                for line in f:
-                    if line.startswith("MemTotal:"):
-                        kb = int(line.split()[1])
-                        return round(kb / 1024**2, 1)
-        except Exception:
-            pass
+    except (AttributeError, ImportError, OSError, RuntimeError, ValueError):
+        pass
+
+    # Fallback: read from /proc/meminfo on Linux.
+    try:
+        with open("/proc/meminfo") as f:
+            for line in f:
+                if line.startswith("MemTotal:"):
+                    kb = int(line.split()[1])
+                    return round(kb / 1024**2, 1)
+    except (OSError, ValueError):
+        pass
+
+    # macOS and other POSIX systems generally expose physical RAM via sysconf.
+    try:
+        pages = os.sysconf("SC_PHYS_PAGES")
+        page_size = os.sysconf("SC_PAGE_SIZE")
+        if pages > 0 and page_size > 0:
+            return round(pages * page_size / 1024**3, 1)
+    except (AttributeError, OSError, ValueError):
+        pass
     return 0.0