Add --base-url flag to serve command for correct feed links

src/server.py

@@ -7,7 +7,7 @@ from src.db import get_connection
 from src.rss import generate_feed, generate_index_html
 
 
-def create_handler(db_path: str):
+def create_handler(db_path: str, base_url: str = None):
     """Factory that returns an HTTP request handler class bound to a DB path."""
 
     class FeedHandler(BaseHTTPRequestHandler):
@@ -64,6 +64,8 @@ def create_handler(db_path: str):
                 pass
 
         def _base_url(self) -> str:
+            if base_url:
+                return base_url
             host = self.server.server_address[0]
             port = self.server.server_address[1]
             return f"http://{host}:{port}"