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/gitian-descriptors/README.md

@@ -1,4 +1,8 @@
-### Gavin's notes on getting gitian builds up and running using KVM:###
+### Notes on getting gitian builds up and running using KVM:###
+
+Note: These are legacy notes inherited from upstream. The real, supported DragonX
+build path is `./build.sh` together with the `depends/` system; gitian is legacy
+and is retained here only for historical reference.
 
 These instructions distilled from:
 [  https://help.ubuntu.com/community/KVM/Installation](  https://help.ubuntu.com/community/KVM/Installation)
@@ -20,7 +24,7 @@ Sanity checks:
 
 Once you've got the right hardware and software:
 
-    git clone git://github.com/bitcoin/bitcoin.git
+    git clone https://git.dragonx.is/DragonX/dragonx.git
     git clone git://github.com/devrandom/gitian-builder.git
     mkdir gitian-builder/inputs
     cd gitian-builder/inputs
@@ -62,5 +66,5 @@ Here's a description of Gavin's setup on OSX 10.6:
 5. Still inside Ubuntu, tell gitian-builder to use LXC, then follow the "Once you've got the right hardware and software" instructions above:
 
 	export USE_LXC=1
-	git clone git://github.com/bitcoin/bitcoin.git
+	git clone https://git.dragonx.is/DragonX/dragonx.git
 	... etc