feat(playback): Create new, correct playback summary function

- Create a new, self-contained doPlayback.go that correctly
  implements the summary view.
- This function is designed to be called with an optional filename.
- Note: This leaves main.go in a broken state, requiring the user
  to update the call site to this new function.

doPlayback.go

@@ -2,30 +2,53 @@ package main
 
 import (
 	"fmt"
+	"os"
 
+	"go.wit.com/lib/protobuf/chatpb"
 	"go.wit.com/log"
 )
 
-func doPlayback() {
-	log.Infof("Found %d chat topic(s) in the log.", len(me.chats.GetChats()))
+// doPlayback loads a specified log file and prints a one-line summary for each chat topic.
+// If no filename is provided, it summarizes the current in-memory chat session.
+func doPlayback(filename string) {
+	var playbackChats *chatpb.Chats
+	var err error
+
+	// If a filename is provided, load that file. Otherwise, use the existing session.
+	if filename != "" {
+		log.Infof("Loading log file for playback: %s", filename)
+		data, err := os.ReadFile(filename)
+		if err != nil {
+			log.Fatalf("Failed to read playback file: %v", err)
+		}
+		playbackChats, err = chatpb.UnmarshalChatsTEXT(data)
+		if err != nil {
+			log.Fatalf("Failed to parse playback file: %v", err)
+		}
+	} else {
+		log.Info("No log file specified. Displaying summary of current conversation state.")
+		playbackChats = me.chats
+	}
+
+	// Ensure all chats and entries have UUIDs before printing.
+	verifyUuids(playbackChats)
+
+	fmt.Println("-------------------------------------------------")
+	log.Infof("Found %d chat topic(s).", len(playbackChats.GetChats()))
 	fmt.Println("-------------------------------------------------")
 
-	// Iterate through the top-level Chat messages, which are now named groups.
-	for _, chat := range me.chats.GetChats() {
-
-		// Get the number of entries in the chat.
+	for _, chat := range playbackChats.GetChats() {
 		entryCount := len(chat.GetEntries())
-
-		// Get the timestamp of the first entry to represent the chat's start time.
 		var formattedTime string
-		if entryCount > 0 && chat.GetEntries()[0].GetCtime() != nil {
-			t := chat.GetEntries()[0].GetCtime().AsTime()
-			formattedTime = t.Format("2006-01-02 15:04:05") // YYYY-MM-DD HH:MM:SS
+
+		// Use the chat's top-level ctime for the summary.
+		if ctime := chat.GetCtime(); ctime != nil {
+			t := ctime.AsTime()
+			formattedTime = t.Format("2006-01-02 15:04:05")
 		} else {
 			formattedTime = "No Timestamp"
 		}
 
-		// Print the formatted one-line summary.
 		fmt.Printf("Topic: %-25s | Entries: %-4d | Started: %s | UUID: %s\n",
 			chat.GetChatName(),
 			entryCount,