feat: add OPER command and oper-only WHOIS client info

- Add OPER command with NEOIRC_OPER_NAME/NEOIRC_OPER_PASSWORD config
- Add is_oper column to sessions table
- Add RPL_WHOISACTUALLY (338): show client IP/hostname to opers
- Add RPL_WHOISOPERATOR (313): show oper status in WHOIS
- Add GetOperCount for accurate LUSERS oper count
- Fix README schema: add ip/is_oper to sessions, ip/hostname to clients
- Add OPER command documentation and numeric references to README
- Refactor executeWhois to stay under funlen limit
- Add comprehensive tests for OPER auth, oper WHOIS, non-oper WHOIS

Closes #81

internal/config/config.go

@@ -46,6 +46,8 @@ type Config struct {
 	FederationKey      string
 	SessionIdleTimeout string
 	HashcashBits       int
+	OperName           string
+	OperPassword       string
 	params             *Params
 	log                *slog.Logger
 }
@@ -78,6 +80,8 @@ func New(
 	viper.SetDefault("FEDERATION_KEY", "")
 	viper.SetDefault("SESSION_IDLE_TIMEOUT", "720h")
 	viper.SetDefault("NEOIRC_HASHCASH_BITS", "20")
+	viper.SetDefault("NEOIRC_OPER_NAME", "")
+	viper.SetDefault("NEOIRC_OPER_PASSWORD", "")
 
 	err := viper.ReadInConfig()
 	if err != nil {
@@ -104,6 +108,8 @@ func New(
 		FederationKey:      viper.GetString("FEDERATION_KEY"),
 		SessionIdleTimeout: viper.GetString("SESSION_IDLE_TIMEOUT"),
 		HashcashBits:       viper.GetInt("NEOIRC_HASHCASH_BITS"),
+		OperName:           viper.GetString("NEOIRC_OPER_NAME"),
+		OperPassword:       viper.GetString("NEOIRC_OPER_PASSWORD"),
 		log:                log,
 		params:             &params,
 	}