Add configurable max hops filter for auto-add contacts

Filter auto-add of new contacts by hop count (issues #1533, #1546).
Setting is configurable from the companion app via extended
CMD_SET/GET_AUTOADD_CONFIG protocol (0 = no limit, 1-63 = max hops).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

examples/companion_radio/NodePrefs.h

@@ -30,4 +30,5 @@ struct NodePrefs {  // persisted to file
   uint8_t autoadd_config;    // bitmask for auto-add contacts config
   uint8_t client_repeat;
   uint8_t path_hash_mode;    // which path mode to use when sending
+  uint8_t autoadd_max_hops;  // 0 = no limit, 1-63 = max hops for auto-add
 };