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.

pyproject.toml

@@ -1,6 +1,6 @@
 [project]
 name = "browser-cli"
-version = "0.12.0"
+version = "0.12.1"
 description = "Control your real running browser from the terminal or Python SDK"
 requires-python = ">=3.10"
 dependencies = [
@@ -8,6 +8,7 @@ dependencies = [
     "cryptography>=48",
     "rich>=13",
     "msgpack>=1",
+    "httpx>=0.28",
 ]
 
 [project.optional-dependencies]