Add module READMEs, .gitignore, and remove Bin/ from tracking

Add README.md for each library module documenting API, platform
backends, and usage. Add .gitignore for build artifacts. Remove
pre-built binaries from version control.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ZNet/README.md

@@ -0,0 +1,42 @@
+# ZNet
+
+Event-driven UDP networking library for multiplayer games, built on top of
+libsst-net and enet.
+
+## Architecture
+
+- `ZNetServer` -- listens for connections, manages multiple peers
+- `ZNetClient` -- connects to a single server
+- `ZNetHost` -- shared base class for both
+- `ZNetPeer` -- represents a remote connection
+
+## Packet delivery
+
+Packets are created with `ZNetHost::CreatePacket()` and sent with either
+reliable or transient (fire-and-forget) delivery:
+
+- `ZNET_RELIABLE` -- guaranteed delivery with sequencing and ACK
+- `ZNET_TRANSIENT` -- unreliable, lowest latency
+
+Packets larger than MTU are automatically fragmented and reassembled.
+
+## Events
+
+Poll with `HasEvent()` / `GetNextEvent()`:
+
+| Event | Meaning |
+|---|---|
+| `ZNETEVENT_CONNECT` | Peer connected |
+| `ZNETEVENT_DISCONNECT` | Peer disconnected gracefully |
+| `ZNETEVENT_TIMEOUT` | Peer timed out |
+| `ZNETEVENT_DATA` | Data packet received |
+
+## Features
+
+- Bandwidth throttling (token bucket) via `ZNetBandwidthMeter`
+- Configurable MTU (512 -- 1500 bytes, with IPv4/IPv6 safe defaults)
+- Packet loss simulation for testing (`SetDropChance`)
+- Connection validation callback on server (`ZNetConnectCallback`)
+- Up to 4 listen sockets per server
+- Reference-counted packets
+- `ZNetUtil::ReaderForPacket()` / `WriterForPacket()` for easy serialization