Replace domain with more info for YouTube+Twitter

In topic listings, when a link topic is from YouTube or Twitter, this
will now display more info about the "source" instead of just the
domain. For YouTube, the channel name is displayed, and for Twitter, the
author of the tweet is displayed.

tildes/tildes/models/topic/topic.py

@@ -361,6 +361,26 @@ class Topic(DatabaseModel):
         # parsing it from the link if it's not present
         return self.get_content_metadata("domain") or get_domain_from_url(self.link)
 
+    @property
+    def link_source(self) -> str:
+        """Return the link's "source", which can be defined for certain domains.
+
+        If special behavior isn't defined for a domain, this just falls back to
+        returning the domain itself.
+        """
+        if not self.is_link_type:
+            raise ValueError("Non-link topics do not have a link source")
+
+        domain = self.link_domain
+        authors = self.get_content_metadata("authors")
+
+        if domain == "twitter.com" and authors:
+            return f"Twitter: @{authors[0]}"
+        elif domain == "youtube.com" and authors:
+            return f"YouTube: {authors[0]}"
+
+        return domain
+
     @property
     def is_spoiler(self) -> bool:
         """Return whether the topic is marked as a spoiler."""

tildes/tildes/templates/macros/topics.jinja2

@@ -83,7 +83,7 @@
       {% if topic.is_user_treated_as_source %}
         aria-label="Posted by">{{ username_linked(topic.user.username) }}
       {% else %}
-        aria-label="Link domain">{{ topic.link_domain }}
+        aria-label="Link source">{{ topic.link_source }}
       {% endif %}
       </div>