docs: update README for new endpoints, fix config name, remove dead field

- Document POST /api/v1/logout endpoint
- Document GET /api/v1/users/me endpoint
- Add 'users' field to GET /api/v1/server response docs
- Fix config: SESSION_TIMEOUT -> SESSION_IDLE_TIMEOUT
- Update storage section: session expiry is implemented
- Update roadmap: move session expiry to implemented
- Remove dead SessionTimeout config field from Go code

internal/config/config.go

@@ -31,7 +31,6 @@ type Config struct {
 	Port               int
 	SentryDSN          string
 	MaxHistory         int
-	SessionTimeout     int
 	MaxMessageSize     int
 	MOTD               string
 	ServerName         string
@@ -62,7 +61,6 @@ func New(
 	viper.SetDefault("METRICS_USERNAME", "")
 	viper.SetDefault("METRICS_PASSWORD", "")
 	viper.SetDefault("MAX_HISTORY", "10000")
-	viper.SetDefault("SESSION_TIMEOUT", "86400")
 	viper.SetDefault("MAX_MESSAGE_SIZE", "4096")
 	viper.SetDefault("MOTD", "")
 	viper.SetDefault("SERVER_NAME", "")
@@ -87,7 +85,6 @@ func New(
 		MetricsUsername:    viper.GetString("METRICS_USERNAME"),
 		MetricsPassword:    viper.GetString("METRICS_PASSWORD"),
 		MaxHistory:         viper.GetInt("MAX_HISTORY"),
-		SessionTimeout:     viper.GetInt("SESSION_TIMEOUT"),
 		MaxMessageSize:     viper.GetInt("MAX_MESSAGE_SIZE"),
 		MOTD:               viper.GetString("MOTD"),
 		ServerName:         viper.GetString("SERVER_NAME"),