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

src/hush_globals.h

@@ -102,7 +102,7 @@ int32_t ASSETCHAINS_OVERWINTER = -1;
 int32_t ASSETCHAINS_STAKED;
 uint64_t ASSETCHAINS_COMMISSION,ASSETCHAINS_SUPPLY = 10,ASSETCHAINS_FOUNDERS_REWARD;
 uint32_t HUSH_INITDONE;
-char HUSHUSERPASS[8192+512+1],BTCUSERPASS[8192]; uint16_t HUSH3_PORT = 18031,BITCOIND_RPCPORT = 18031;
+char HUSHUSERPASS[8192+512+1],BTCUSERPASS[8192]; uint16_t DRAGONX_PORT = 21769,BITCOIND_RPCPORT = 21769;
 uint64_t PENDING_HUSH_TX;
 extern int32_t HUSH_LOADINGBLOCKS;
 unsigned int MAX_BLOCK_SIGOPS = 20000;