fix(extension): keep user-opened tabs free & fix agent-tab leak on session stop (issue #57)

- session_stop: exclude tabs still tracked in agentCreatedTabs from the
  release decision so a tab that failed to close is no longer mistaken for
  a user tab (which previously kept the window open and leaked the tab).
- Distinguish user-created tabs from agent-created tabs in the Agent Window
  via a pending-tab counter consumed by chrome.tabs.onCreated, so tabs the
  user opens themselves (new-tab button / Cmd+T / open in new tab) are never
  taken over by the BrowserSkill control mask.
- background overlay: decide per-tab state BEFORE showing controls
  (overlayStateForTab + pushOverlayStateForTab) so a user tab receives hidden
  on its first overlay.ready ping instead of flashing control then hiding.
- AgentWindowApi.ensureActiveTab now resolves with the activated/created tab
  id instead of void, so SessionManager can record homeTabId. This fixes the
  tsc failure flagged in review (the interface previously returned
  Promise<void> while callers treated the result as number | null).
- Wire the production tabManagement.tabs / tabsQuery deps into
  tool.session_stop, both in the dispatcher and in the disconnect cleanup.
  They were never injected, which left the agent-tab cleanup and the
  window-release path as dead code outside tests (behaviour identical to
  main). Added a dispatcher-level integration test that fails without the
  wiring: a surviving user tab must release the window, not close it.

apps/extension/src/tools/tabs.ts

@@ -426,9 +426,18 @@ export async function handleTabCreate(
   const paramErr = validateTabCreateParams(params);
   if (paramErr) return paramErr;
 
+  // Flag the pending agent tab *before* create so the chrome.tabs.onCreated
+  // listener (background.ts) can tell this tab apart from a user-opened tab.
+  manager.markAgentTabPending(ctx.agentWindowId);
+
   const tab = await createTabAndCleanup(deps, buildCreateProps(ctx, params));
   if (isRpcError(tab)) return tab;
 
+  // Track agent-created tabs so session_stop can clean them up (design §3.1).
+  // The onCreated listener also adds this id; this is an idempotent fallback
+  // in case the listener has not fired yet.
+  ctx.agentCreatedTabs.add(tab.id);
+
   return {
     tab_id: tab.id,
     window_id: ctx.agentWindowId,
@@ -526,6 +535,9 @@ export async function handleTabClose(
   }
   try {
     await getTabsApi(deps).remove(params.tab_id);
+    // Keep the tracking set accurate so session_stop won't try to close a
+    // tab that's already gone (design §3.1).
+    ctx.agentCreatedTabs.delete(params.tab_id);
   } catch (err) {
     return {
       code: "protocol_error",