fix: show the container hostname in the shell prompt

Coolify injects HOST=0.0.0.0 into every compose app, and zsh seeds $HOST and
the %m/%M prompt escapes from that variable rather than calling gethostname().
The prompt read "0", the first dot-separated field of 0.0.0.0, even though the
container hostname itself was set correctly.

Pass the hostname in as HOST alongside the hostname: key, both from a single
SERVICE_HOSTNAME variable. Neither service reads HOST itself -- code-server
binds [::]:8443, Paseo binds PASEO_LISTEN -- so this only affects the prompt.

Not named HOSTNAME: Compose interpolation lets the deploying shell's
environment win over the .env file, and HOSTNAME is set in every container,
including the one Coolify runs in.

PASEO_LABEL is renamed to SERVICE_HOSTNAME; it was never a Paseo variable.
The example git identity is blanked out along with it.

code-server/compose.yml

@@ -1,11 +1,13 @@
 services:
   code-server:
     image: 'lscr.io/linuxserver/code-server:latest'
-    hostname: miti99-cs
+    hostname: ${SERVICE_HOSTNAME}
     environment:
       - PUID=1000
       - PGID=1000
       - TZ=Asia/Ho_Chi_Minh
+      # Hostname zsh's prompt reads, overriding the one Coolify injects.
+      - HOST=${SERVICE_HOSTNAME}
       - DEFAULT_WORKSPACE=/config/workspace
       - PWA_APPNAME=code-server
       - 'DOCKER_MODS=linuxserver/mods:universal-package-install|linuxserver/mods:universal-docker|linuxserver/mods:code-server-golang|linuxserver/mods:code-server-nodejs|linuxserver/mods:code-server-npmglobal|linuxserver/mods:code-server-pnpm|linuxserver/mods:code-server-python3|linuxserver/mods:code-server-zsh'