adding new extract command to extract selector or main content as markdown, updateing version as 0.5.0

browser_cli/__init__.py

@@ -247,6 +247,9 @@ class BrowserCLI:
     def extract_json(self, selector: str):
         return self._cmd("extract.json", {"selector": selector})
 
+    def extract_markdown(self, selector: str | None = None) -> str:
+        return self._cmd("extract.markdown", {"selector": selector}) or ""
+
     # ── Session ───────────────────────────────────────────────────────────
 
     def session_save(self, name: str) -> None: