Install: Hekate 8GB after copy (fuse >4GiB), dram_fuse helper, RAM test target

- Add dram_fuse.c/h for shared fuse-to-MiB mapping
- After successful update/clean install copy: if hekate_8gb.bin exists and
  fuse reports more than 4 GiB, copy to sd:/payload.bin and
  sd:/bootloader/update.bin, then remove source; otherwise remove helper only
- Makefile: make ram-test builds output/RAM-Test.bin (tools/ram_test_main.c)

Made-with: Cursor

source/dram_fuse.h

@@ -0,0 +1,6 @@
+#pragma once
+
+#include <utils/types.h>
+
+/* DRAM capacity in MiB from fuse DRAM ID + SoC (same table as RAM test payload). */
+int dram_capacity_mib_from_fuse(void);