feat: implement Tier 1 channel modes (+o/+v/+m/+t), KICK, NOTICE

Implement core IRC channel functionality:

1. Channel member flags: is_operator and is_voiced columns in
   channel_members table (proper boolean columns per sneak's
   instruction, not text string modes).

2. MODE +o/+v/-o/-v: Grant/revoke operator and voice status.
   Permission-checked (only +o can grant). NAMES replies show
   @nick for operators and +nick for voiced users.

3. MODE +m (moderated): Only +o and +v users can send PRIVMSG
   or NOTICE to moderated channels. Others get ERR_CANNOTSENDTOCHAN.

4. MODE +t (topic lock): Only +o can change topic when active.
   Default ON for new channels (standard IRC behavior). Others
   get ERR_CHANOPRIVSNEEDED.

5. KICK command: Operator-only, removes user from channel,
   broadcasts to all members including kicked user.

6. NOTICE differentiation: No RPL_AWAY auto-reply, skips hashcash
   validation on +H channels per RFC 2812.

Additional improvements:
- Channel creator auto-gets +o on first JOIN
- ISUPPORT now advertises PREFIX=(ov)@+ and CHANMODES=,,H,mnst
- MODE query shows accurate +nt/+m/+H mode string
- Fixed pre-existing unparam lint issue in fanOutSilent

Includes 22 new tests covering all requirements.

closes #85

pkg/irc/commands.go

@@ -4,6 +4,7 @@ package irc
 const (
 	CmdAway    = "AWAY"
 	CmdJoin    = "JOIN"
+	CmdKick    = "KICK"
 	CmdList    = "LIST"
 	CmdLusers  = "LUSERS"
 	CmdMode    = "MODE"