Rebrand hush3 to DragonX: binaries, defaults, and build system

- 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 via
  RandomXDatasetManager, 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

.gitignore

@@ -167,4 +167,8 @@ REGTEST_7776
 src/cc/librogue.so
 src/cc/games/prices
 src/cc/games/tetris
-release-linux/
+release-linux/
+release/
+src/dragonxd
+src/dragonx-cli
+src/dragonx-tx