chore(setup): build miner from DragonX/drg-xmrig and rename staging dir

setup.sh now clones/builds the miner from git.dragonx.is/DragonX/drg-xmrig
(was dragonx/xmrig-hac), and the prebuilt staging dir is renamed
prebuilt-binaries/xmrig-hac -> prebuilt-binaries/drg-xmrig across build.sh, the
legacy Windows build script, .gitignore and README.

Also aligns setup.sh's section-8 directory list with section 7 (it previously
used a bare "xmrig" token, creating a stray empty prebuilt-binaries/xmrig/),
and updates the xmrig_manager.cpp header comment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scripts/legacy/build-windows.sh

@@ -256,8 +256,8 @@ HEADER_START
         echo -e "${YELLOW}Note: Daemon binaries not found in prebuilt-binaries/dragonxd-win/ — wallet only${NC}"
     fi
 
-    # ── xmrig binary (from prebuilt-binaries/xmrig-hac/) ────────────────
-    XMRIG_DIR="$SCRIPT_DIR/prebuilt-binaries/xmrig-hac"
+    # ── xmrig binary (from prebuilt-binaries/drg-xmrig/) ────────────────
+    XMRIG_DIR="$SCRIPT_DIR/prebuilt-binaries/drg-xmrig"
     if [ -f "$XMRIG_DIR/xmrig.exe" ]; then
         cp -f "$XMRIG_DIR/xmrig.exe" "$EMBED_RES_DIR/xmrig.exe"
         echo "  Staged xmrig.exe ($(du -h "$XMRIG_DIR/xmrig.exe" | cut -f1))"