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

contrib/debian/control

@@ -1,18 +1,18 @@
-Source: hush
+Source: dragonx
 Section: utils
 Priority: optional
-Maintainer: Hush <myhushteam@gmail.com>
-Homepage: https://hush.is
+Maintainer: DragonX <dan-s-dev@proton.me>
+Homepage: https://dragonx.is
 Build-Depends: autoconf, automake, bsdmainutils, build-essential,
  cmake, curl, git, g++-multilib, libc6-dev, libsodium-dev,
  libtool, m4, ncurses-dev, pkg-config, python,
  unzip, wget, zlib1g-dev
-Vcs-Git: https://git.hush.is/hush/hush3.git
-Vcs-Browser: https://git.hush.is/hush/hush3
+Vcs-Git: https://git.dragonx.is/DragonX/dragonx.git
+Vcs-Browser: https://git.dragonx.is/DragonX/dragonx
 
-Package: hush
+Package: dragonx
 Architecture: amd64 arm64
 Depends: ${shlibs:Depends}
-Description: Cryptocoin full node for Hush
- Speak And Transact Freely with Hush, which inherits from Bitcoin Protocol and
- Zcash Protocol and is focused on private communications.
+Description: Privacy-focused cryptocurrency full node for DragonX
+ DragonX is a privacy-focused cryptocurrency using RandomX proof-of-work.
+ All transactions are shielded by default. Fork of the Hush Full Node.