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/extension.py

@@ -1,16 +1,16 @@
 """Extension-control namespace: ``b.extension.*``."""
 from __future__ import annotations
 
-from browser_cli.sdk.base import Namespace
+from browser_cli.sdk.base import Namespace, sdk_command
 
 class ExtensionNS(Namespace):
-    """Control the browser-cli extension itself."""
+  """Control the browser-cli extension itself."""
 
-    def reload(self) -> None:
-        """Reload the browser-cli extension service worker.
+  @sdk_command("extension.reload")
+  def reload(self) -> None:
+    """Reload the browser-cli extension service worker.
 
-        Schedules a ``chrome.runtime.reload()`` inside the extension and returns
-        immediately. The extension restarts ~200 ms later and reconnects via the
-        keepalive alarm within ~25 seconds.
-        """
-        self._c._cmd("extension.reload", {})
+    Schedules a ``chrome.runtime.reload()`` inside the extension and returns
+    immediately. The extension restarts ~200 ms later and reconnects via the
+    keepalive alarm within ~25 seconds.
+    """