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/sdl_checkpoints.pl

@@ -3,7 +3,8 @@
 # Distributed under the GPLv3 software license, see the accompanying
 # file COPYING or https://www.gnu.org/licenses/gpl-3.0.en.html
 
-# This script is used to generate the data used by the silentdragonlite-cli checkpoints.rs file
+# This script is used to generate the data used by a light-wallet checkpoints.rs file.
+# The checkpoint format follows the upstream silentdragonlite-cli reference:
 # https://git.hush.is/hush/silentdragonlite-cli/src/branch/master/lib/src/lightclient/checkpoints.rs#L24
 
 use warnings;
@@ -12,16 +13,16 @@ use strict;
 # call this script like this to generate checkpoints for another chain:
 # CLI=./src/hac-cli ./contrib/sdl_checkpoints.pl ...
 
-my $hush    = $ENV{CLI} || "./src/hush-cli";
-my $gethash = "$hush getblockhash";
-my $gettree = "$hush getblockmerkletree";
+my $cli     = $ENV{CLI} || "./src/dragonx-cli";
+my $gethash = "$cli getblockhash";
+my $gettree = "$cli getblockmerkletree";
 my $start   = shift || 300000;
 my $end     = shift || 840000;
 my $stride  = shift || 10000;
 
-my $blocks  = qx{$hush getblockcount};
+my $blocks  = qx{$cli getblockcount};
 if($?) {
-    print "ERROR, is hushd running? exiting...\n";
+    print "ERROR, is dragonxd running? exiting...\n";
     exit 1;
 }