Fix ARM64 ISO: patch mkarchiso EFI FAT size for large ARM64 kernel

The ARM64 kernel Image is ~50 MB. mkarchiso calculates the EFI FAT
image size as int(total_bytes/MiB)+2, which leaves no room for FAT
filesystem overhead → "Disk full" when copying the kernel in.

Patch mkarchiso at container startup (before mkarchiso runs) to use
+128 MiB buffer instead, giving plenty of headroom.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/docker/entrypoint-arm64.sh

@@ -729,7 +729,30 @@ echo "OrionOS ARM64 customization complete."
 CUSTOMIZE
 chmod 755 "$PROFILE/airootfs/root/customize_airootfs.sh"
 
-# ── 13. Build the ISO ─────────────────────────────────────────────────
+# ── 13. Patch mkarchiso EFI FAT image size ───────────────────────────
+# The ARM64 kernel (Image) is ~50 MB. mkarchiso's default size formula is
+# int(total_bytes/1024/1024)+2 MiB, which leaves no room for FAT overhead
+# and causes "Disk full". Bump the buffer to +128 MiB.
+python3 - <<'PYEOF'
+import re, sys
+with open('/usr/bin/mkarchiso') as f:
+    txt = f.read()
+orig = txt
+# Match: int($1 / 1024 / 1024) + N  (with any spacing or small N)
+txt = re.sub(
+    r'int\(\$1\s*/\s*1024\s*/\s*1024\s*\)\s*\+\s*\d+',
+    r'int($1 / 1024 / 1024) + 128',
+    txt
+)
+if txt == orig:
+    print('mkarchiso: FAT size pattern not found — build may fail with Disk full', file=sys.stderr)
+else:
+    with open('/usr/bin/mkarchiso', 'w') as f:
+        f.write(txt)
+    print('mkarchiso: patched EFI FAT size buffer to +128 MiB')
+PYEOF
+
+# ── 14. Build the ISO ─────────────────────────────────────────────────
 echo ">>> Building ARM64 ISO (this takes 5-15 minutes)..."
 mkdir -p "$DIST" "$WORK"