Rebrand hush3 to DragonX and share RandomX dataset across mining threads

Minimal rebrand (see compliant-rebrand branch for full rebrand):
- Rename binaries: hushd/hush-cli/hush-tx → dragonxd/dragonx-cli/dragonx-tx
- Default to DRAGONX chain params without -ac_* flags (randomx, blocktime=36, private=1)
- Update configure.ac: AC_INIT([DragonX],[1.0.0])
- Update client version string and user-agent to /DragonX:1.0.0/
- Add chainparams.cpp with DRAGONX network parameters
- Update build.sh, miner.cpp, pow.cpp for DragonX
- Add bootstrap-dragonx.sh utility script
- Update .gitignore for release directory

Share single RandomX dataset across all mining threads:
- Add RandomXDatasetManager with readers-writer lock, reducing RAM from
  ~2GB per thread to ~2GB total plus ~2MB per thread for the VM scratchpad
- Add LogProcessMemory() diagnostic helper for Linux and Windows

util/build-win.sh

@@ -40,4 +40,4 @@ cd $WD
 
 sed -i 's/-lboost_system-mt /-lboost_system-mt-s /' configure
 cd src/
-CC="${CC} -g " CXX="${CXX} -g " make V=1  hushd.exe hush-cli.exe hush-tx.exe
+CC="${CC} -g " CXX="${CXX} -g " make V=1  dragonxd.exe dragonx-cli.exe dragonx-tx.exe