Bot: DM+channel modes with separate replies; buzzer auto-mute; UX fixes

- Bot redesign: DM bot active for all private messages (no pubkey filter),
  channel bot optional with separate enable flag; both can run simultaneously
- Bot: one shared trigger, separate reply texts for DM and channel
- Buzzer: add Auto mode (mutes when BT connected, unmutes on disconnect);
  per-channel force-on overrides still work as intended
- Settings: defer flash writes to menu exit (only when dirty)
- Settings: add Seconds toggle (hide clock seconds, refresh drops 1s→60s)
- Fullscreen msg preview: fix truncation (fmsg buf 79→140 chars)
- RingtoneEditor: fix melody playback cut after first note (RTTTL lib holds
  pointer — moved play buffer to member variable)
- BotScreen: remove key hint footer
- .gitattributes: protect README.md from upstream merge conflicts

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

examples/companion_radio/ui-new/UITask.h

@@ -111,6 +111,8 @@ public:
   }
 
   void toggleBuzzer();
+  void cycleBuzzerMode();   // ON → OFF → Auto → ON
+  int  getBuzzerMode(); // 0=ON, 1=OFF, 2=Auto
   bool getGPSState();
   void toggleGPS();
   void applyBrightness();