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/handlers/api_test.go

@@ -12,6 +12,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"path/filepath"
+	"strconv"
 	"strings"
 	"sync"
 	"testing"
@@ -115,8 +116,9 @@ func newTestServer(
 
 func newTestGlobals() *globals.Globals {
 	return &globals.Globals{
-		Appname: "neoirc-test",
-		Version: "test",
+		Appname:   "neoirc-test",
+		Version:   "test",
+		StartTime: time.Now(),
 	}
 }
 
@@ -466,8 +468,11 @@ func findNumeric(
 	msgs []map[string]any,
 	numeric string,
 ) bool {
+	want, _ := strconv.Atoi(numeric)
+
 	for _, msg := range msgs {
-		if msg[commandKey] == numeric {
+		code, ok := msg["code"].(float64)
+		if ok && int(code) == want {
 			return true
 		}
 	}