fix: IRC SPA cleanup — /motd, /query, Firefox / key, default MOTD

- Add default MOTD with figlet-style ASCII art for neoirc
- Add MOTD server command so /motd can be re-requested
- Add /motd client command to display message of the day
- Add /query command to open DM tabs with optional message
- Add /clear command to clear messages in current tab
- Fix Firefox quick search conflict: global keydown handler
  captures '/' and redirects focus to the input element
- Auto-focus input on SPA init and tab changes
- Show MOTD on resumed sessions (new sessions get it from
  server automatically during creation)
- Update /help with new commands
- Style MOTD on login screen for better ASCII art display

internal/handlers/api.go

@@ -670,6 +670,13 @@ func (hdlr *Handlers) dispatchCommand(
 		hdlr.handleQuit(
 			writer, request, sessionID, nick, body,
 		)
+	case "MOTD":
+		hdlr.deliverMOTD(
+			request, clientID, sessionID, nick,
+		)
+		hdlr.respondJSON(writer, request,
+			map[string]string{"status": "ok"},
+			http.StatusOK)
 	case "PING":
 		hdlr.respondJSON(writer, request,
 			map[string]string{