Configure full MQTT topics in the private INI

Use configured topics for commands, state, availability and Last Will. Replace shared installation prefixes with generic examples. Validate configuration before stopping an existing service; add tests for custom and invalid topics.

meshcore-phone-mode.ini.example

@@ -1,4 +1,4 @@
-# Zorruno — MeshCore Phone App Mode v1.0 — 2026-10-03
+# Zorruno — MeshCore Phone App Mode v1.1 — 2026-10-03
 # Copy to /etc/meshcore-phone-mode.ini; installer creates it with mode 0600.
 # Enter the MQTT credentials locally. Values are literal (no surrounding quotes).
 # Keep username/password blank only if your broker permits anonymous access.
@@ -7,6 +7,13 @@ host = 127.0.0.1
 port = 1883
 username =
 password =
+client_id = meshcore-phone-mode
+
+# Full topic names; choose your own and use the same values in Home Assistant.
+# All three are required and must be different, without + or # wildcards.
+command_topic = meshcore/phone_app_mode/set
+state_topic = meshcore/phone_app_mode/state
+availability_topic = meshcore/phone_app_mode/availability
 
 [controller]
 poll_seconds = 15