cleanup: rebrand currency unit, depends mirrors, seeds; drop Hush-history files

Follow-up to the doc rebrand, addressing the previously out-of-scope legacy:

- Currency unit: strCurrencyUnits (chainparams.cpp) and CURRENCY_UNIT
  (amount.cpp) "HUSH" -> "DRAGONX". Both are display-only (RPC help + metrics);
  no logic comparisons, verified.
- depends mirrors: libsodium/boost/utfcpp fetched from git.hush.is/attachments;
  repointed to canonical upstream (GitHub release / archives.boost.io / GitHub
  tag) with the existing sha256 hashes verified to match those sources.
- Seeds: nodes_main.txt now lists the five node[1-5].dragonx.is IPs (DNS-resolved)
  instead of Hush nodes; regenerated src/chainparamsseeds.h (was compiling Hush
  seed IPs as the fixed fallback); generate-seeds.py header now says DragonX;
  hush_seed_nodes.txt updated to DragonX seeds.
- Deleted Hush-history / wrong-for-DragonX files: contrib/snapshot/ (block-500000
  Hush airdrop, ~10MB), notary_seeds.txt (Hush notaries; DragonX isn't notarized),
  and the Hush emission scripts hush_supply, hush_supply_old, hush_halvings,
  hush_block_subsidy_per_halving (hardcode Hush's 340000/12.5 economics).

Kept: hush_scanner (engine invoked by dragonx_scanner) and the "The Hush
developers" copyright headers (lineage credit).

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

contrib/seeds/generate-seeds.py

@@ -167,9 +167,9 @@ def main():
     g.write('// Instead, update contrib/seeds/nodes_main.txt then run\n')
     g.write('//    ./contrib/seeds/generate-seeds.py contrib/seeds > src/chainparamsseeds.h\n')
     g.write('// OR run: make seeds\n')
-    g.write('#ifndef HUSH_CHAINPARAMSSEEDS_H\n')
-    g.write('#define HUSH_CHAINPARAMSSEEDS_H\n')
-    g.write('// List of fixed seed nodes for the Hush network\n')
+    g.write('#ifndef DRAGONX_CHAINPARAMSSEEDS_H\n')
+    g.write('#define DRAGONX_CHAINPARAMSSEEDS_H\n')
+    g.write('// List of fixed seed nodes for the DragonX network\n')
     g.write('// Each line contains a BIP155 serialized address.\n')
     g.write('//\n')
     with open(os.path.join(indir,'nodes_main.txt'), 'r', encoding="utf8") as f:

contrib/seeds/nodes_main.txt

@@ -1,38 +1,14 @@
-# node1.hush.is
-103.69.128.148
+# node1.dragonx.is
+212.56.41.63
 
-# node2.hush.is
-194.29.100.179
+# node2.dragonx.is
+194.140.198.176
 
-# node3.hush.is
-45.132.75.69
+# node3.dragonx.is
+212.56.41.47
 
-# node4.hush.is
-170.205.39.39
+# node4.dragonx.is
+144.126.147.165
 
-# lite.hushpool.is
-149.28.102.219
-
-# lite2.hushpool.is
-155.138.228.68
-
-# wtfistheinternet.hush.is
-107.174.70.251
-
-# arrakis.hush.is
-178.250.189.141
-
-# torv3
-b2dln7mw7ydnuopls444tuixujhcw5kn5o22cna6gqfmw2fl6drb5nad.onion
-dslbaa5gut5kapqtd44pbg65tpl5ydsamfy62hjbldhfsvk64qs57pyd.onion
-vsqdumnh5khjbrzlxoeucbkiuaictdzyc3ezjpxpp2ph3gfwo2ptjmyd.onion
-
-# ipv6
-2a0c:b641:6f1:18e::2
-2406:ef80:3:1269::1
-2406:ef80:2:3b59::1
-2406:ef80:1:146e::1
-2406:ef80:4:2132::1
-
-# i2p
-7oumuppuzgbzlkahavx7qrtjnvbhkixjqdmeg7f6fhndgfhz7mlq.b32.i2p
+# node5.dragonx.is
+176.126.87.241