Pi bundle: drop the informational .env keys

KVITT_PI_HOST and KVITT_PI_SSH_USER were read by nothing on the Pi (D-103).
They are gone from .env.example; the README's scp, ssh and NPM steps use
<user>@<kvitt-pi-address> and the Kvitt Pi's LAN IPv4 address in words.
install.sh checks only the keys the stack reads, so an older .env that still
has the two keys installs unchanged.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

infra/pi/compose.yaml

@@ -24,7 +24,7 @@ services:
     security_opt:
       - no-new-privileges:true
     mem_limit: 160m
-    # On all interfaces of the Pi: NPM on the Home Assistant Pi connects to <KVITT_PI_HOST>:8080 over the LAN.
+    # On all interfaces of the Pi: NPM on the Home Assistant Pi connects to this Pi's LAN address, port 8080.
     ports:
       - "8080:8080"
     environment: