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/perf.py

@@ -1,19 +1,23 @@
 """Performance and background-jobs namespace: ``b.perf.*``."""
 from __future__ import annotations
 
-from browser_cli.sdk.base import Namespace
+from browser_cli.sdk.base import Namespace, sdk_command
 
 class PerfNS(Namespace):
-    """Inspect the performance profile and manage background jobs."""
+  """Inspect the performance profile and manage background jobs."""
 
-    def status(self) -> dict:
-        return self._c._cmd("perf.status", {}) or {}
+  @sdk_command("perf.status", default={})
+  def status(self) -> dict:
+    """Return current performance profile, throttle info, and running jobs."""
 
-    def set_profile(self, profile: str) -> dict:
-        return self._c._cmd("perf.set_profile", {"profile": profile}) or {}
+  @sdk_command("perf.set_profile", lambda self, profile: {"profile": profile}, default={})
+  def set_profile(self, profile: str) -> dict:
+    """Set the global extension performance profile."""
 
-    def job_status(self, job_id: str) -> dict:
-        return self._c._cmd("jobs.status", {"jobId": job_id}) or {}
+  @sdk_command("jobs.status", lambda self, job_id: {"jobId": job_id}, default={})
+  def job_status(self, job_id: str) -> dict:
+    """Return status/progress for a background job."""
 
-    def job_cancel(self, job_id: str) -> dict:
-        return self._c._cmd("jobs.cancel", {"jobId": job_id}) or {}
+  @sdk_command("jobs.cancel", lambda self, job_id: {"jobId": job_id}, default={})
+  def job_cancel(self, job_id: str) -> dict:
+    """Request cancellation for a background job."""