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/session.py

@@ -1,63 +1,64 @@
 """Session namespace: ``b.session.*``."""
 from __future__ import annotations
 
-from browser_cli.sdk.base import Namespace
+from browser_cli.sdk.base import Namespace, sdk_command
+
+def _load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs) -> dict:
+  return {
+    "name": name,
+    "gentleMode": gentle_mode,
+    "discardBackgroundTabs": discard_background_tabs,
+    "lazy": lazy,
+    "eagerTabs": eager_tabs,
+  }
 
 class SessionNS(Namespace):
-    """Save, restore, list, and diff browser sessions."""
+  """Save, restore, list, and diff browser sessions."""
 
-    def save(self, name: str) -> dict:
-        """Save all current tabs as session *name*. Returns the save result (incl. tab count)."""
-        return self._c._cmd("session.save", {"name": name}) or {}
+  @sdk_command("session.save", lambda self, name: {"name": name}, default={})
+  def save(self, name: str) -> dict:
+    """Save all current tabs as session *name*. Returns the save result (incl. tab count)."""
 
-    @staticmethod
-    def _load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs) -> dict:
-        return {
-            "name": name,
-            "gentleMode": gentle_mode,
-            "discardBackgroundTabs": discard_background_tabs,
-            "lazy": lazy,
-            "eagerTabs": eager_tabs,
-        }
+  def load(
+    self,
+    name: str,
+    *,
+    gentle_mode: str = "auto",
+    discard_background_tabs: bool = False,
+    lazy: bool = False,
+    eager_tabs: int = 10,
+  ) -> dict:
+    """Restore session *name*. Returns the load result (incl. tabs opened)."""
+    return self.command("session.load", _load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs)) or {}
 
-    def load(
-        self,
-        name: str,
-        *,
-        gentle_mode: str = "auto",
-        discard_background_tabs: bool = False,
-        lazy: bool = False,
-        eager_tabs: int = 10,
-    ) -> dict:
-        """Restore session *name*. Returns the load result (incl. tabs opened)."""
-        args = self._load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs)
-        return self._c._cmd("session.load", args) or {}
+  def load_background(
+    self,
+    name: str,
+    *,
+    gentle_mode: str = "auto",
+    discard_background_tabs: bool = False,
+    lazy: bool = False,
+    eager_tabs: int = 10,
+  ) -> dict:
+    """Restore session *name* as a background job. Returns the job descriptor."""
+    args = _load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs)
+    return self.command("session.load", {**args, "__background": True}) or {}
 
-    def load_background(
-        self,
-        name: str,
-        *,
-        gentle_mode: str = "auto",
-        discard_background_tabs: bool = False,
-        lazy: bool = False,
-        eager_tabs: int = 10,
-    ) -> dict:
-        """Restore session *name* as a background job. Returns the job descriptor."""
-        args = self._load_args(name, gentle_mode, discard_background_tabs, lazy, eager_tabs)
-        return self._c._cmd("session.load", {**args, "__background": True}) or {}
+  @sdk_command("session.diff", lambda self, name_a, name_b: {"nameA": name_a, "nameB": name_b}, default={})
+  def diff(self, name_a: str, name_b: str) -> dict:
+    """Diff two saved sessions."""
 
-    def diff(self, name_a: str, name_b: str) -> dict:
-        return self._c._cmd("session.diff", {"nameA": name_a, "nameB": name_b}) or {}
+  def list(self) -> list[dict]:
+    """Return saved sessions.
 
-    def list(self) -> list[dict]:
-        """Return saved sessions.
+    In implicit multi-browser mode each session dict includes a ``browser`` key.
+    """
+    return self.multi_list("session.list", {}, self.tag_browser)
 
-        In implicit multi-browser mode each session dict includes a ``browser`` key.
-        """
-        return self._c._multi_list("session.list", {}, self._c._tag_browser)
+  @sdk_command("session.remove", lambda self, name: {"name": name}, return_result=False)
+  def remove(self, name: str) -> None:
+    """Remove a saved session."""
 
-    def remove(self, name: str) -> None:
-        self._c._cmd("session.remove", {"name": name})
-
-    def auto_save(self, enabled: bool) -> None:
-        self._c._cmd("session.auto_save", {"enabled": enabled})
+  @sdk_command("session.auto_save", lambda self, enabled: {"enabled": enabled}, return_result=False)
+  def auto_save(self, enabled: bool) -> None:
+    """Enable or disable automatic session saves."""