Redo backend installer logic to support BIOS/MBR boot on older devices and switch to GRUB2

iridium_installer/ui/pages/partitioning.py

@@ -54,8 +54,13 @@ def get_total_memory() -> int:
     return 0
 
 
+def is_uefi():
+    return os.path.exists("/sys/firmware/efi")
+
+
 def calculate_auto_partitions(disk_device):
     disk_size = 0
+    uefi = is_uefi()
     try:
         # Get disk size in bytes
         result = subprocess.run(
@@ -83,16 +88,21 @@ def calculate_auto_partitions(disk_device):
     disk_mb = disk_size / (1024 * 1024)
 
     # Defaults
-    efi_size = 2 * 1024 * 1024 * 1024
+    efi_size = 1024 * 1024 * 1024 if uefi else 0
     swap_size = ram_size + (2 * 1024 * 1024 * 1024)
     min_root_size = 10 * 1024 * 1024 * 1024  # 10GB
 
+    # Cap swap for auto-calc if disk is small
+    if disk_size < 100 * 1024**3:
+        swap_size = min(swap_size, 4 * 1024**3)
+
     total_required = efi_size + swap_size + min_root_size
 
     use_swap = True
 
     if disk_size < total_required:
-        efi_size = 1 * 1024 * 1024 * 1024
+        if uefi:
+            efi_size = 512 * 1024 * 1024
         use_swap = False
         swap_size = 0
         if disk_size < (efi_size + min_root_size):
@@ -101,26 +111,28 @@ def calculate_auto_partitions(disk_device):
 
     root_size = disk_size - efi_size - swap_size
 
-    partitions = [
-        {
+    partitions = []
+    
+    if uefi:
+        partitions.append({
             "type": "partition",
             "name": "EFI System",
             "filesystem": "vfat",
-            "mount_point": "/boot",
+            "mount_point": "/boot/efi",
             "size": f"{efi_size / (1024**3):.1f} GB",
             "bytes": efi_size,
             "style_class": "part-efi",
-        },
-        {
-            "type": "partition",
-            "name": "Root",
-            "filesystem": "ext4",
-            "mount_point": "/",
-            "size": f"{root_size / (1024**3):.1f} GB",
-            "bytes": root_size,
-            "style_class": "part-root",
-        },
-    ]
+        })
+
+    partitions.append({
+        "type": "partition",
+        "name": "Root",
+        "filesystem": "ext4",
+        "mount_point": "/",
+        "size": f"{root_size / (1024**3):.1f} GB",
+        "bytes": root_size,
+        "style_class": "part-root",
+    })
 
     if use_swap:
         partitions.append(