Add client tag accessor to NdbNote

Add a clientTag property to NdbNote that parses and returns the client
tag metadata from an event's tags, enabling display of which app
published an event.

Ref: https://github.com/damus-io/damus/issues/3323
Signed-off-by: alltheseas <alltheseas@users.noreply.github.com>

nostrdb/NdbNote.swift

@@ -470,6 +470,19 @@ extension NdbNote {
     public var references: References<RefId> {
         References<RefId>(tags: self.tags)
     }
+
+    /// Parses and returns the client tag metadata if present on this note.
+    var clientTag: ClientTagMetadata? {
+        for tag in tags {
+            guard tag.count >= 2, tag[0].matches_str("client") else {
+                continue
+            }
+            if let metadata = ClientTagMetadata(tagComponents: tag.strings()) {
+                return metadata
+            }
+        }
+        return nil
+    }
     
     func thread_reply() -> ThreadReply? {
         if self.known_kind != .highlight {