docs: rebrand documentation, packaging, and helper scripts to DragonX

The docs/packaging were largely un-rebranded Hush3 content, with several
docs stating facts that are wrong for DragonX. This rewrites them against
the verified DragonX source state.

Corrections (not just branding):
- PoW: RandomX (CPU), not Equihash/ASIC — README, overview.md, randomx.md
- Privacy: private from genesis (ac_private=1, Sapling@height1), not "as of
  block 340000" — overview.md, payment-api.md
- Removed the false "coinbase must be shielded" consensus claim
  (shield-coinbase.md, payment-api.md); coinbase is directly spendable
- Fixed default fee 0.0001 (was 0.0010000, 10x); stratum port 22769 (was 19031)
- datadir ~/.hush/DRAGONX, DRAGONX.conf, dragonxd/dragonx-cli/dragonx-tx,
  git.dragonx.is throughout; branch model dev->dragonx
- Softened the inherited dPoW reorg claim (no live DragonX notary infra)

Packaging: fix build-debian-package.sh + gen-manpages.sh to use the dragonx
binaries/manpages; rename bash-completions to dragonx*; drop hush-arrakis-chain
from the package. Keep /usr/share/hush (hardcoded in the binary for params).

Also: README links/logo, ObsidianDragon + SilentDragonXAndroid wallets,
networking/init/dev-process/contrib/util rebrand, and leftover helper scripts.
Delete legacy duplicates (hushd.* init/service, HUSH3.conf examples,
OLD_WALLETS.md, hsc.md) and rename hush-uri.bat -> dragonx-uri.bat.

Out of scope (noted, not changed): historical changelog/copyright, the Hush
mainnet airdrop snapshot, seed data files, depends/ source mirrors, and the
in-code strCurrencyUnits="HUSH".

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

contrib/dragonxd.bash-completion

@@ -0,0 +1,58 @@
+# bash programmable completion for dragonxd(1)
+# Copyright (c) 2012-2017 The Bitcoin Core developers
+# Copyright (c) 2016-2017 The Zcash developers
+# Copyright (c) 2018      The Hush developers
+# Distributed under the GPLv3 software license, see the accompanying
+# file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
+
+_dragonxd() {
+    local cur prev words=() cword
+    local dragonxd
+
+    # save and use original argument to invoke dragonxd for -help
+    # it might not be in $PATH
+    dragonxd="$1"
+
+    COMPREPLY=()
+    _get_comp_words_by_ref -n = cur prev words cword
+
+    case "$cur" in
+        -conf=*|-pid=*|-loadblock=*|-rpccookiefile=*|-wallet=*)
+            cur="${cur#*=}"
+            _filedir
+            return 0
+            ;;
+        -datadir=*|-exportdir=*)
+            cur="${cur#*=}"
+            _filedir -d
+            return 0
+            ;;
+        -*=*)	# prevent nonsense completions
+            return 0
+            ;;
+        *)
+
+            # only parse -help if senseful
+            if [[ -z "$cur" || "$cur" =~ ^- ]]; then
+                local helpopts
+                helpopts=$($dragonxd -help 2>&1 | awk '$1 ~ /^-/ { sub(/=.*/, "="); print $1 }' )
+                COMPREPLY=( $( compgen -W "$helpopts" -- "$cur" ) )
+            fi
+
+            # Prevent space if an argument is desired
+            if [[ $COMPREPLY == *= ]]; then
+                compopt -o nospace
+            fi
+            return 0
+            ;;
+    esac
+} &&
+complete -F _dragonxd dragonxd
+
+# Local variables:
+# mode: shell-script
+# sh-basic-offset: 4
+# sh-indent-comment: t
+# indent-tabs-mode: nil
+# End:
+# ex: ts=4 sw=4 et filetype=sh