feat: implement IRC numerics batch 2 — connection registration, channel ops, user queries

Add comprehensive IRC numeric reply support:

Connection registration (001-005):
- 002 RPL_YOURHOST, 003 RPL_CREATED, 004 RPL_MYINFO, 005 RPL_ISUPPORT
- All sent automatically during session creation after RPL_WELCOME

Server statistics (251-255):
- RPL_LUSERCLIENT, RPL_LUSEROP, RPL_LUSERCHANNELS, RPL_LUSERME
- Sent during connection registration and via LUSERS command

Channel operations:
- MODE command: query channel modes (324 RPL_CHANNELMODEIS, 329 RPL_CREATIONTIME)
- MODE command: query user modes (221 RPL_UMODEIS)
- NAMES command: query channel member list (353/366)
- LIST command: list all channels (322 RPL_LIST, 323 end of list)

User queries:
- WHOIS command: 311/312/318/319 numerics
- WHO command: 352 RPL_WHOREPLY, 315 RPL_ENDOFWHO

Database additions:
- GetChannelCount, ListAllChannelsWithCounts
- GetChannelCreatedAt, GetSessionCreatedAt

Also adds StartTime to Globals for RPL_CREATED and updates README
with comprehensive documentation of all new commands and numerics.

closes #52

internal/handlers/api_test.go

@@ -115,8 +115,9 @@ func newTestServer(
 
 func newTestGlobals() *globals.Globals {
 	return &globals.Globals{
-		Appname: "neoirc-test",
-		Version: "test",
+		Appname:   "neoirc-test",
+		Version:   "test",
+		StartTime: time.Now(),
 	}
 }