refactor: reorganize client transport and extension internals

- Split client, native, remote, serve, markdown, and SDK internals into focused packages with direct imports.
- Move local and remote transport framing/protocol helpers behind clearer module boundaries.
- Break up the extension injected DOM logic into a separate content dispatch bundle and dedicated content modules.
- Add explicit client handling for passive remote discovery without noisy PQ warnings.
- Keep behavior covered with updated unit, integration, and extension tests.

browser_cli/sdk/windows.py

@@ -1,24 +1,26 @@
 """Windows namespace: ``b.windows.*``."""
 from __future__ import annotations
 
-from browser_cli.sdk.base import Namespace
+from browser_cli.sdk.base import Namespace, sdk_command
 
 class WindowsNS(Namespace):
-    """List, open, close, and rename browser windows."""
+  """List, open, close, and rename browser windows."""
 
-    def list(self) -> list[dict]:
-        """Return browser windows.
+  def list(self) -> list[dict]:
+    """Return browser windows.
 
-        In implicit multi-browser mode each window dict includes a ``browser`` key.
-        """
-        return self._c._multi_list("windows.list", {}, self._c._tag_browser)
+    In implicit multi-browser mode each window dict includes a ``browser`` key.
+    """
+    return self.multi_list("windows.list", {}, self.tag_browser)
 
-    def open(self, url: str | None = None) -> dict:
-        """Open a new browser window, optionally on a URL."""
-        return self._c._cmd("windows.open", {"url": url}) or {}
+  @sdk_command("windows.open", lambda self, url=None: {"url": url}, default={})
+  def open(self, url: str | None = None) -> dict:
+    """Open a new browser window, optionally on a URL."""
 
-    def close(self, window_id: int) -> None:
-        self._c._cmd("windows.close", {"windowId": window_id})
+  @sdk_command("windows.close", lambda self, window_id: {"windowId": window_id}, return_result=False)
+  def close(self, window_id: int) -> None:
+    """Close a browser window by ID."""
 
-    def rename(self, window_id: int, name: str) -> None:
-        self._c._cmd("windows.rename", {"windowId": window_id, "name": name})
+  @sdk_command("windows.rename", lambda self, window_id, name: {"windowId": window_id, "name": name}, return_result=False)
+  def rename(self, window_id: int, name: str) -> None:
+    """Rename a browser window."""