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>

util/checkpoints.pl

@@ -7,7 +7,7 @@ use strict;
 
 # Generate checkpoint data for use in src/chainparams.cpp
 my $perday  = 1152;
-my $cli     = "./src/hush-cli";
+my $cli     = "./src/dragonx-cli";
 my $stride  = shift || 1000;
 if ($stride =~ m/help/) {
     print "To generate checkpoint data every 1000 blocks: $0 &> checkpoints.txt\n";
@@ -34,7 +34,7 @@ if ($acname) {
     # HSC's by default have a blocktime of 60s
     $perday = 1440;
 } else {
-    $acname = 'HUSH3';
+    $acname = 'DRAGONX';
 }
 
 my $gethash = "$cli getblockhash";
@@ -49,7 +49,7 @@ my $last    = 0;
 my $now     = time();
 chomp($blocks);
 
-print "// Generated at $now via hush3 util/checkpoints.pl by Duke Leto\n";
+print "// Generated at $now via dragonx util/checkpoints.pl\n";
 
 while (1) {
 	$count++;