Add DEPLOY.md: ports, firewall, RPC credentials, SSL, operation

Also fix the COIN default in docs/environment.rst, and refer to the Palladium
node setup by concept instead of by paths of its repository.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

docs/environment.rst

@@ -192,7 +192,7 @@ These environment variables are optional:
 .. envvar:: COIN
 
   Must be a :attr:`NAME` from one of the :class:`Coin` classes in
-  `lib/coins.py`_.  Defaults to ``Bitcoin``.
+  `lib/coins.py`_.  Defaults to ``Palladium``.
 
 .. envvar:: NET