Mock TCP server cannot show a data stream and uses a different port from the relay default

Describe the bug
src/server/src/main.rs performs a single stream.read into a 1024-byte buffer with no loop, then returns and drops the connection. As a stand-in for iMotions it therefore shows only the first packet, which is the one thing it is needed for.

It also binds 127.0.0.1:7878 while the relay's placeholder is 127.0.0.1:9999, so it is not a drop-in target.

Expected behavior
It reads in a loop until the peer closes, and prints each \r\n-terminated packet, so a contributor without an iMotions license can watch live output.

Additional context
This is the fallback path documented in the README for contributors without iMotions access, so it matters for onboarding. Also stream.peer_addr().unwrap() at line 35 can panic the accept loop, and stream.write at line 17 does not handle partial writes.

Found while writing the setup documentation in #138 / #178.