feat: add IRCv3 cap negotiation, channel management, state persistence

Implement CAP LS 302 flow with configurable ircv3_caps list, replacing
the minimal SASL-only registration. Parse IRCv3 message tags (@key=value)
with proper value unescaping. Add channel management plugin (kick, ban,
unban, topic, mode) and bot API methods. Add SQLite key-value StateStore
for plugin state persistence with !state inspection command.

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

docs/CHEATSHEET.md

@@ -68,6 +68,37 @@ admins = ["*!~user@trusted.host", "ops!*@*.ops.net"]
 
 IRC operators are auto-detected via WHO. Hostmask patterns use fnmatch.
 
+## Channel Management (admin)
+
+```
+!kick nick reason          # Kick user from channel
+!ban *!*@bad.host          # Ban hostmask
+!unban *!*@bad.host        # Remove ban
+!topic New topic text      # Set channel topic
+!topic                     # Query current topic
+!mode +m                   # Set channel mode
+!mode +o nick              # Give ops
+```
+
+## State Store (admin)
+
+```
+!state list myplugin       # List keys
+!state get myplugin key    # Get value
+!state del myplugin key    # Delete key
+!state clear myplugin      # Clear all keys
+```
+
+## IRCv3 Capabilities
+
+```toml
+# config/derp.toml
+[server]
+ircv3_caps = ["multi-prefix", "away-notify", "server-time"]
+```
+
+SASL auto-added when sasl_user/sasl_pass configured.
+
 ## Plugin Management (admin)
 
 ```
@@ -232,6 +263,7 @@ msg.is_channel  # True if channel
 msg.prefix      # nick!user@host
 msg.command     # PRIVMSG, JOIN, etc.
 msg.params      # All params list
+msg.tags        # IRCv3 tags dict
 ```
 
 ## Config Locations