fix: replace CI2PSession (process-I2P) with CI2PEmbedded in merged code

Merge left residual references to the SAMI-PC process-based I2P API
(CI2PSession, fI2P) in files that now compile against the v6 embedded
I2P (CI2PEmbedded). Fixed:
- net.cpp ConnectNode: removed fI2P/CI2PSession blocks, restored
  v6 SOCKS-proxy connection path (I2P routing handled in netbase)
- CMakeLists.txt: removed i2p.cpp/i2p_process.cpp from build (not
  part of embedded I2P; kept in tree as reference only)
- rpcnet.cpp: CI2PSession → CI2PEmbedded (IsRunning/GetI2PAddress)
- rpcwallet.cpp: same API migration
- init.cpp: same API migration for startup address print

src/init.cpp

@@ -1706,7 +1706,7 @@ bool AppInit2()
             StartupPerfLog("i2p_start", GetTimeMillis() - nI2PStart, strprintf("started=%d", i2pStarted));
             if (i2pStarted) {
                 SetReachable(NET_I2P, true);
-                std::string i2pAddr = CI2PSession::GetInstance()->GetB32Address();
+                std::string i2pAddr = CI2PEmbedded::GetInstance()->GetI2PAddress();
                 printf("I2P network enabled. Our address: %s\n", i2pAddr.c_str());
             } else {
                 printf("NOTICE: I2P not available this session; continuing with Tor only\n");