feat(stealth): silent operation — never steal the user's foreground tab

Driving the user's real Chrome should not yank their view around. Now the agent
operates entirely in the background:
- New tabs are created with `background: true` (CreateTargetParams) so opening
  one never foregrounds it (the ab-connect extension already used active:false;
  this covers the raw-CDP path too).
- Dropped the two AUTO `Page.bringToFront` calls (auto-connect fresh tab, and the
  internal active-page switch). The explicit `bringToFront` command is untouched —
  surfacing a tab stays opt-in.
- enable_domains now sets `Emulation.setFocusEmulationEnabled(true)` so a
  backgrounded agent tab still renders (screenshots work), isn't render-throttled,
  and reports document.hasFocus()/visibilityState='visible' — which also removes
  the "tab is hidden the whole session" bot tell.

Verified headless: hasFocus=true/visible while backgrounded; click + screenshot
still work. Default behaviour, no flag.

cli/src/native/actions.rs

@@ -1511,12 +1511,11 @@ pub async fn execute_command(cmd: &Value, state: &mut DaemonState) -> Value {
 /// subsequent navigations don't hijack the user's existing tabs.
 async fn connect_auto_with_fresh_tab() -> Result<BrowserManager, String> {
     let mut mgr = BrowserManager::connect_auto().await?;
+    // tab_new creates the tab in the background (CreateTargetParams.background),
+    // so attaching to the user's Chrome never steals their foreground tab. We
+    // deliberately do NOT bring it to front — silent operation.
     mgr.tab_new(None, None).await?;
     let session_id = mgr.active_session_id()?.to_string();
-    let _ = mgr
-        .client
-        .send_command("Page.bringToFront", None, Some(&session_id))
-        .await;
 
     // Liveness probe: confirm the CDP session can actually round-trip
     // before returning success. Without this, a zombie CDP socket (process