Compliant rebrand: legal compliance, code audit, and documentation (Phases 0-3)

Phase 0 - Legal Compliance:
- COPYING: Add DragonX copyright, preserve all upstream attributions
- AUTHORS: Add DragonX developers section
- LICENSE: Restore standard FSF GPLv3 text (fix GNU→GENERAL error)
- Add DragonX copyright headers to all 21 modified source files
- contrib/debian/copyright: Add DragonX attribution
- README.md: Add GPLv3 Section 5(a) attribution section

Phase 1 - init.cpp Cleanup:
- PID file: hushd.pid → dragonxd.pid
- Shutdown thread: hush-shutoff → dragonx-shutoff
- Debug message: stopping HUSH → stopping DragonX

Phase 2 - HUSH3/ishush3 Code Audit:
- Rename ishush3 → isdragonx across ~15 source files
- Update "HUSH3" chain-identity checks to "DRAGONX" in consensus,
  difficulty, notarization, devtax, and RPC code
- Intentionally preserve cross-chain "HUSH3" refs (gateway, notary dest)
- Build verified: all three binaries compile cleanly

Phase 3 - Documentation:
- README.md: Full rewrite with DragonX chain params, build instructions
- Man pages: Create dragonxd.1, dragonx-cli.1, dragonx-tx.1 (v1.0.0)
- Doc files: Add beefy-DRAGONX.conf, dragonxd-systemd.md, dragonxd.service
- Init scripts: Create dragonxd.{conf,init,openrc,openrcconf,service}
- Debian packaging: Update control, changelog, install, manpages, examples
- Update doc/init.md and contrib/init/README.md

src/util.cpp

@@ -1,6 +1,7 @@
 // Copyright (c) 2009-2010 Satoshi Nakamoto
 // Copyright (c) 2009-2014 The Bitcoin Core developers
 // Copyright (c) 2016-2025 The Hush developers
+// Copyright (c) 2024-2026 The DragonX developers
 // Distributed under the GPLv3 software license, see the accompanying
 // file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
 
@@ -750,7 +751,7 @@ void ReadConfigFile(map<string, string>& mapSettingsRet,
 #ifndef _WIN32
 boost::filesystem::path GetPidFile()
 {
-    boost::filesystem::path pathPidFile(GetArg("-pid", "hushd.pid"));
+    boost::filesystem::path pathPidFile(GetArg("-pid", "dragonxd.pid"));
     if (!pathPidFile.is_complete()) pathPidFile = GetDataDir() / pathPidFile;
     return pathPidFile;
 }