Add SD logging and update docs

- Add optional microSD CSV logging per sender/day on receiver
- Wire logger into receiver packet handling
- Document new batch header fields, build envs, and SD logging
- Make sender links open in a new tab

src/web_server.cpp

@@ -52,7 +52,8 @@ static String render_sender_block(const SenderStatus &status) {
       }
     }
   }
-  s += "<strong>" + String(status.last_data.device_id) + "</strong>";
+  String device_id = status.last_data.device_id;
+  s += "<strong><a href='/sender/" + device_id + "' target='_blank' rel='noopener noreferrer'>" + device_id + "</a></strong>";
   if (status.has_data && status.last_data.link_valid) {
     s += " RSSI:" + String(status.last_data.link_rssi_dbm) + " SNR:" + String(status.last_data.link_snr_db, 1);
   }