android: fix QR join flow + cleanup log levels + remove log artifacts

- MainActivity: call NativeLib.joinChannel directly (bypass ViewModel null repo)
- LogManager: add Log.d for Kotlin logs visibility in logcat
- ChatViewModel/NativeLib: add diagnostic logs for join path
- chat_sync: JNI-safe logs via __android_log_print, add error on !g_cs
- etcp_debug: DUMP INFO→DEBUG (remove 99.8% packet spam)
- secure_channel/etcp_connections/topo_node: keepalive PING/PONG spam INFO→DEBUG
- .gitignore: logreceiver output + build artifacts
- Remove tracked log files and build dir from repo

.gitignore

@@ -86,6 +86,10 @@ tests/bench_*
 *.log
 utun.log*
 
+# logreceiver artifacts
+tools/logreceiver/logreceiver_output.log*
+tools/logreceiver/build/
+
 # Local configs
 *.cfg
 !utun_test.cfg