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.

extension/src/content/page-info.ts

@@ -0,0 +1,14 @@
+export function pageInfo() {
+  const metas: Record<string, string> = {};
+  document.querySelectorAll("meta[name], meta[property]").forEach(m => {
+    const k = m.getAttribute("name") || m.getAttribute("property");
+    if (k) metas[k] = m.getAttribute("content") || "";
+  });
+  return {
+    title: document.title,
+    url: location.href,
+    readyState: document.readyState,
+    lang: document.documentElement.lang || null,
+    meta: metas,
+  };
+}