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

LICENSE

@@ -1,4 +1,4 @@
-                    GENERAL GENERAL PUBLIC LICENSE
+                    GNU GENERAL PUBLIC LICENSE
                        Version 3, 29 June 2007
 
  Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>
@@ -7,15 +7,15 @@
 
                             Preamble
 
-  The GENERAL General Public License is a free, copyleft license for
+  The GNU General Public License is a free, copyleft license for
 software and other kinds of works.
 
   The licenses for most software and other practical works are designed
 to take away your freedom to share and change the works.  By contrast,
-the GENERAL General Public License is intended to guarantee your freedom to
+the GNU General Public License is intended to guarantee your freedom to
 share and change all versions of a program--to make sure it remains free
 software for all its users.  We, the Free Software Foundation, use the
-GENERAL General Public License for most of our software; it applies also to
+GNU General Public License for most of our software; it applies also to
 any other work released this way by its authors.  You can apply it to
 your programs, too.
 
@@ -37,7 +37,7 @@ freedoms that you received.  You must make sure that they, too, receive
 or can get the source code.  And you must show them these terms so they
 know their rights.
 
-  Developers that use the GENERAL GPL protect your rights with two steps:
+  Developers that use the GNU GPL protect your rights with two steps:
 (1) assert copyright on the software, and (2) offer you this License
 giving you legal permission to copy, distribute and/or modify it.
 
@@ -72,7 +72,7 @@ modification follow.
 
   0. Definitions.
 
-  "This License" refers to version 3 of the GENERAL General Public License.
+  "This License" refers to version 3 of the GNU General Public License.
 
   "Copyright" also means copyright-like laws that apply to other kinds of
 works, such as semiconductor masks.
@@ -549,35 +549,35 @@ to collect a royalty for further conveying from those to whom you convey
 the Program, the only way you could satisfy both those terms and this
 License would be to refrain entirely from conveying the Program.
 
-  13. Use with the GENERAL Affero General Public License.
+  13. Use with the GNU Affero General Public License.
 
   Notwithstanding any other provision of this License, you have
 permission to link or combine any covered work with a work licensed
-under version 3 of the GENERAL Affero General Public License into a single
+under version 3 of the GNU Affero General Public License into a single
 combined work, and to convey the resulting work.  The terms of this
 License will continue to apply to the part which is the covered work,
-but the special requirements of the GENERAL Affero General Public License,
+but the special requirements of the GNU Affero General Public License,
 section 13, concerning interaction through a network will apply to the
 combination as such.
 
   14. Revised Versions of this License.
 
   The Free Software Foundation may publish revised and/or new versions of
-the GENERAL General Public License from time to time.  Such new versions will
+the GNU General Public License from time to time.  Such new versions will
 be similar in spirit to the present version, but may differ in detail to
 address new problems or concerns.
 
   Each version is given a distinguishing version number.  If the
-Program specifies that a certain numbered version of the GENERAL General
+Program specifies that a certain numbered version of the GNU General
 Public License "or any later version" applies to it, you have the
 option of following the terms and conditions either of that numbered
 version or of any later version published by the Free Software
 Foundation.  If the Program does not specify a version number of the
-GENERAL General Public License, you may choose any version ever published
+GNU General Public License, you may choose any version ever published
 by the Free Software Foundation.
 
   If the Program specifies that a proxy can decide which future
-versions of the GENERAL General Public License can be used, that proxy's
+versions of the GNU General Public License can be used, that proxy's
 public statement of acceptance of a version permanently authorizes you
 to choose that version for the Program.