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>

docs/USAGE.md

@@ -82,59 +82,78 @@ Configure your IRC client to connect to the bouncer:
 |---------|-------|
 | Server | `127.0.0.1` |
 | Port | `6667` (or as configured) |
-| Password | `networkname:yourpassword` |
+| Password | `yourpassword` |
 
 ### Password Format
 
 ```
-PASS <network>:<password>
+PASS <password>
 ```
 
-- `network` -- matches a `[networks.NAME]` section in config
-- `password` -- the `bouncer.password` value from config
-
-If you omit the network prefix (`PASS yourpassword`), the first configured
-network is used.
+The password is the `bouncer.password` value from config. A single connection
+automatically attaches to **all** configured networks.
 
 ### Client Examples
 
 **irssi:**
 ```
-/connect -password libera:mypassword 127.0.0.1 6667
+/connect -password mypassword 127.0.0.1 6667
 ```
 
 **weechat:**
 ```
-/server add bouncer 127.0.0.1/6667 -password=libera:mypassword
+/server add bouncer 127.0.0.1/6667 -password=mypassword
 /connect bouncer
 ```
 
 **hexchat:**
 
-Set server password to `libera:mypassword` in the network settings.
+Set server password to `mypassword` in the network settings.
 
-## Multiple Networks
+## Multi-Network Namespacing
 
-Define multiple `[networks.*]` sections in the config. Each gets its own
-persistent server connection through the SOCKS5 proxy.
-
-Connect your client with the appropriate network prefix:
+All configured networks are multiplexed onto a single client connection. Channels
+and nicks carry a `/network` suffix so you can tell which network they belong to:
 
 ```
-PASS libera:mypassword    # connects to [networks.libera]
-PASS oftc:mypassword      # connects to [networks.oftc]
+Client sees:         Server wire:
+#libera/libera  <->  #libera       (on libera network)
+#debian/oftc    <->  #debian       (on oftc network)
+user123/libera  <->  user123       (on libera network)
 ```
 
-Multiple clients can attach to the same network simultaneously. All receive
-the same messages in real time.
+### Rules
+
+- **Channels**: `#channel/network` in client, `#channel` on wire
+- **Foreign nicks**: `nick/network` in client, `nick` on wire
+- **Own nicks**: shown without suffix (prevents client confusion)
+- **Sending messages**: include the `/network` suffix in the target
+
+```
+/msg #libera/libera hello     -> sends "hello" to #libera on libera network
+/join #test/oftc              -> joins #test on oftc network
+/msg user123/libera hi        -> private message to user123 on libera
+```
+
+### Comma-Separated JOIN/PART
+
+Targets can span networks:
+
+```
+/join #a/libera,#b/oftc       -> joins #a on libera AND #b on oftc
+```
+
+Multiple clients can attach simultaneously. All receive the same namespaced
+messages in real time.
 
 ## What Clients Receive on Connect
 
-When a client authenticates and attaches to a network:
+When a client authenticates:
 
-1. **Backlog replay** -- missed messages since last disconnect
-2. **Synthetic welcome** -- 001-004 numeric replies from the bouncer
-3. **Channel state** -- TOPIC and NAMES for each joined channel
+1. **Backlog replay** -- missed messages (namespaced) from all networks
+2. **Synthetic welcome** -- 001-004 numeric replies listing all networks
+3. **Channel state** -- synthetic JOIN, TOPIC, and NAMES for every joined
+   channel across all networks (all namespaced with `/network` suffix)
 
 ## Backlog