feat: multi-network namespace multiplexing

Multiplex all networks onto a single client connection using /network
suffixes on channels and nicks. PASS is now just the password (no
network prefix). Channels appear as #channel/network, foreign nicks as
nick/network, own nicks stay bare.

New namespace.py module with pure encode/decode functions. Router
tracks clients globally (not per-network), namespaces messages before
delivery. Client attaches to all networks on connect, sends synthetic
JOIN/TOPIC/NAMES for every channel across all networks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -4,12 +4,12 @@ IRC bouncer with SOCKS5 proxy support and persistent message backlog.
 
 ## Features
 
-- Connect to multiple IRC networks simultaneously
+- **Multi-network multiplexing**: single client connection sees all networks via `/network` suffixes
 - All outbound connections routed through SOCKS5 proxy
 - Stealth connect: registers with a random pronounceable nick and generic identity
 - Probation window: waits 15s after registration to detect K-lines before revealing real nick
 - Persistent message backlog (SQLite) with replay on reconnect
-- Multiple clients can attach to the same network session
+- Multiple clients can attach simultaneously
 - Password authentication
 - TLS support for IRC server connections
 - Automatic reconnection with exponential backoff
@@ -32,10 +32,18 @@ bouncer -c config/bouncer.toml -v
 From your IRC client, connect to `127.0.0.1:6667` with:
 
 ```
-PASS networkname:yourpassword
+PASS yourpassword
 ```
 
-Where `networkname` matches a `[networks.NAME]` section in your config.
+A single connection gives you all configured networks. Channels and nicks
+appear with a `/network` suffix:
+
+```
+Client sees:         Server sends/receives:
+#libera/libera  <->  #libera       (on libera network)
+#debian/oftc    <->  #debian       (on oftc network)
+user123/libera  <->  user123       (on libera network)
+```
 
 ## How It Works