feat: restore tabs and splits at launch

The tab layout (tab order and names, pins, the active tab, split trees
with their ratios) is saved whenever it changes — checked once a second,
written only on change, so it survives a crash — and reopened at the
next launch: saved profiles reconnect and local shells start in the
directory they were in (on Linux the live /proc cwd, so it isn't one
command behind). Quick Connect tabs and placeholder panes are skipped.
A General setting turns it off; it never runs when launched with
--connect, --run-local or --open, and screenshot runs never save.

Verified: a local tab left in /usr/share came back there with a
'Restored 1 tab(s)' toast.

rust/core/src/service.rs

@@ -127,6 +127,11 @@ impl Service {
         self.sessions.connect_local(&shell)
     }
 
+    /// A local shell with an explicit shell and start directory (restored tabs).
+    pub fn connect_local_in(&self, shell: &str, cwd: Option<PathBuf>) -> String {
+        self.sessions.connect_local_in(shell, cwd)
+    }
+
     pub fn reconnect(&self, id: &str) -> Result<String> {
         self.sessions.reconnect(id)
     }