feat: implement IRC numerics batch 2 — connection registration, channel ops, user queries (#59)

## Summary

Implements the remaining important/commonly-used IRC numeric reply codes, as requested in [issue #52](#52).

### Connection Registration (001-005)
- **002 RPL_YOURHOST** — "Your host is <server>, running version <ver>"
- **003 RPL_CREATED** — "This server was created <date>"
- **004 RPL_MYINFO** — "<server> <version> <usermodes> <chanmodes>"
- **005 RPL_ISUPPORT** — CHANTYPES=#, NICKLEN=32, CHANMODES, NETWORK=neoirc, CASEMAPPING=ascii

All sent automatically after RPL_WELCOME during session creation/login.

### Server Statistics (251-255)
- **251 RPL_LUSERCLIENT** — user count
- **252 RPL_LUSEROP** — operator count
- **254 RPL_LUSERCHANNELS** — channel count
- **255 RPL_LUSERME** — local client count

Sent during connection registration and available via LUSERS command.

### Channel Operations
- **MODE command** — query channel modes (324 RPL_CHANNELMODEIS + 329 RPL_CREATIONTIME) and user modes (221 RPL_UMODEIS)
- **NAMES command** — query channel member list (reuses 353/366)
- **LIST command** — list all channels with member counts (322 RPL_LIST + 323 end)

### User Queries
- **WHOIS command** — 311 RPL_WHOISUSER, 312 RPL_WHOISSERVER, 319 RPL_WHOISCHANNELS, 318 RPL_ENDOFWHOIS
- **WHO command** — 352 RPL_WHOREPLY, 315 RPL_ENDOFWHO

### Database Additions
- `GetChannelCount()` — total channel count for LUSERS
- `ListAllChannelsWithCounts()` — channels with member counts for LIST
- `GetChannelCreatedAt()` — channel creation time for RPL_CREATIONTIME
- `GetSessionCreatedAt()` — session creation time

### Other Changes
- Added `StartTime` to `Globals` struct for RPL_CREATED
- Updated README with comprehensive documentation of all new commands and numerics
- Updated roadmap to reflect implemented features

`docker build .` passes (lint, tests, build all green).

closes [#52](#52)

<!-- session: agent:sdlc-manager:subagent:1f3dcab8-ad6a-4c4c-af72-34a617640c9d -->

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Co-authored-by: clawbot <clawbot@git.eeqj.de>
Reviewed-on: #59
Co-authored-by: clawbot <sneak+clawbot@sneak.cloud>
Co-committed-by: clawbot <sneak+clawbot@sneak.cloud>

internal/irc/numerics.go

@@ -0,0 +1,150 @@
+// Package irc provides constants and utilities for the
+// IRC protocol, including numeric reply codes from
+// RFC 1459 and RFC 2812, and standard command names.
+package irc
+
+// Connection registration replies (001-005).
+const (
+	RplWelcome  = 1
+	RplYourHost = 2
+	RplCreated  = 3
+	RplMyInfo   = 4
+	RplIsupport = 5
+)
+
+// Command responses (200-399).
+const (
+	RplUmodeIs       = 221
+	RplLuserClient   = 251
+	RplLuserOp       = 252
+	RplLuserUnknown  = 253
+	RplLuserChannels = 254
+	RplLuserMe       = 255
+	RplAway          = 301
+	RplUserHost      = 302
+	RplIson          = 303
+	RplUnaway        = 305
+	RplNowAway       = 306
+	RplWhoisUser     = 311
+	RplWhoisServer   = 312
+	RplWhoisOperator = 313
+	RplEndOfWho      = 315
+	RplWhoisIdle     = 317
+	RplEndOfWhois    = 318
+	RplWhoisChannels = 319
+	RplList          = 322
+	RplListEnd       = 323
+	RplChannelModeIs = 324
+	RplCreationTime  = 329
+	RplNoTopic       = 331
+	RplTopic         = 332
+	RplTopicWhoTime  = 333
+	RplInviting      = 341
+	RplWhoReply      = 352
+	RplNamReply      = 353
+	RplEndOfNames    = 366
+	RplBanList       = 367
+	RplEndOfBanList  = 368
+	RplMotd          = 372
+	RplMotdStart     = 375
+	RplEndOfMotd     = 376
+)
+
+// Error replies (400-599).
+const (
+	ErrNoSuchNick        = 401
+	ErrNoSuchServer      = 402
+	ErrNoSuchChannel     = 403
+	ErrCannotSendToChan  = 404
+	ErrTooManyChannels   = 405
+	ErrNoRecipient       = 411
+	ErrNoTextToSend      = 412
+	ErrUnknownCommand    = 421
+	ErrNoNicknameGiven   = 431
+	ErrErroneusNickname  = 432
+	ErrNicknameInUse     = 433
+	ErrUserNotInChannel  = 441
+	ErrNotOnChannel      = 442
+	ErrNotRegistered     = 451
+	ErrNeedMoreParams    = 461
+	ErrAlreadyRegistered = 462
+	ErrChannelIsFull     = 471
+	ErrInviteOnlyChan    = 473
+	ErrBannedFromChan    = 474
+	ErrBadChannelKey     = 475
+	ErrChanOpPrivsNeeded = 482
+)
+
+// names maps numeric codes to their standard IRC names.
+//
+//nolint:gochecknoglobals
+var names = map[int]string{
+	RplWelcome:       "RPL_WELCOME",
+	RplYourHost:      "RPL_YOURHOST",
+	RplCreated:       "RPL_CREATED",
+	RplMyInfo:        "RPL_MYINFO",
+	RplIsupport:      "RPL_ISUPPORT",
+	RplUmodeIs:       "RPL_UMODEIS",
+	RplLuserClient:   "RPL_LUSERCLIENT",
+	RplLuserOp:       "RPL_LUSEROP",
+	RplLuserUnknown:  "RPL_LUSERUNKNOWN",
+	RplLuserChannels: "RPL_LUSERCHANNELS",
+	RplLuserMe:       "RPL_LUSERME",
+	RplAway:          "RPL_AWAY",
+	RplUserHost:      "RPL_USERHOST",
+	RplIson:          "RPL_ISON",
+	RplUnaway:        "RPL_UNAWAY",
+	RplNowAway:       "RPL_NOWAWAY",
+	RplWhoisUser:     "RPL_WHOISUSER",
+	RplWhoisServer:   "RPL_WHOISSERVER",
+	RplWhoisOperator: "RPL_WHOISOPERATOR",
+	RplEndOfWho:      "RPL_ENDOFWHO",
+	RplWhoisIdle:     "RPL_WHOISIDLE",
+	RplEndOfWhois:    "RPL_ENDOFWHOIS",
+	RplWhoisChannels: "RPL_WHOISCHANNELS",
+	RplList:          "RPL_LIST",
+	RplListEnd:       "RPL_LISTEND", //nolint:misspell
+	RplChannelModeIs: "RPL_CHANNELMODEIS",
+	RplCreationTime:  "RPL_CREATIONTIME",
+	RplNoTopic:       "RPL_NOTOPIC",
+	RplTopic:         "RPL_TOPIC",
+	RplTopicWhoTime:  "RPL_TOPICWHOTIME",
+	RplInviting:      "RPL_INVITING",
+	RplWhoReply:      "RPL_WHOREPLY",
+	RplNamReply:      "RPL_NAMREPLY",
+	RplEndOfNames:    "RPL_ENDOFNAMES",
+	RplBanList:       "RPL_BANLIST",
+	RplEndOfBanList:  "RPL_ENDOFBANLIST",
+	RplMotd:          "RPL_MOTD",
+	RplMotdStart:     "RPL_MOTDSTART",
+	RplEndOfMotd:     "RPL_ENDOFMOTD",
+
+	ErrNoSuchNick:        "ERR_NOSUCHNICK",
+	ErrNoSuchServer:      "ERR_NOSUCHSERVER",
+	ErrNoSuchChannel:     "ERR_NOSUCHCHANNEL",
+	ErrCannotSendToChan:  "ERR_CANNOTSENDTOCHAN",
+	ErrTooManyChannels:   "ERR_TOOMANYCHANNELS",
+	ErrNoRecipient:       "ERR_NORECIPIENT",
+	ErrNoTextToSend:      "ERR_NOTEXTTOSEND",
+	ErrUnknownCommand:    "ERR_UNKNOWNCOMMAND",
+	ErrNoNicknameGiven:   "ERR_NONICKNAMEGIVEN",
+	ErrErroneusNickname:  "ERR_ERRONEUSNICKNAME",
+	ErrNicknameInUse:     "ERR_NICKNAMEINUSE",
+	ErrUserNotInChannel:  "ERR_USERNOTINCHANNEL",
+	ErrNotOnChannel:      "ERR_NOTONCHANNEL",
+	ErrNotRegistered:     "ERR_NOTREGISTERED",
+	ErrNeedMoreParams:    "ERR_NEEDMOREPARAMS",
+	ErrAlreadyRegistered: "ERR_ALREADYREGISTERED",
+	ErrChannelIsFull:     "ERR_CHANNELISFULL",
+	ErrInviteOnlyChan:    "ERR_INVITEONLYCHAN",
+	ErrBannedFromChan:    "ERR_BANNEDFROMCHAN",
+	ErrBadChannelKey:     "ERR_BADCHANNELKEY",
+	ErrChanOpPrivsNeeded: "ERR_CHANOPRIVSNEEDED",
+}
+
+// Name returns the standard IRC name for a numeric code
+// (e.g., Name(2) returns "RPL_YOURHOST"). Returns an
+// empty string if the code is unknown.
+func Name(code int) string {
+	return names[code]
+}