support search_syntax in focus_tab

docs/sessions.rst

@@ -159,6 +159,7 @@ all the major keywords you can use in kitty session files:
     launch tail -f /var/log/syslog
 
     # Focus the first tab (index 0) when the session loads
+    # You can also use a match expression like: focus_tab title:logs
     focus_tab 0
 
     # Create a complex layout using multiple splits. Creates two columns of
@@ -279,12 +280,14 @@ documentation for them.
     otherwise the window manager might block changing focus to prevent *focus
     stealing*.
 
-``focus_tab [tab index]``
+``focus_tab [tab specifier]``
     Set which tab should be active (focused) in the current OS Window. The tab
-    index is 0-based, so ``focus_tab 0`` will focus the first tab, ``focus_tab 1``
-    the second tab, and so on. This is useful for session files that create
-    multiple tabs and want to ensure a specific tab is active when the session
-    is loaded.
+    specifier can be either a plain number (treated as a 0-based index) or a
+    match expression. For example, ``focus_tab 0`` will focus the first tab,
+    ``focus_tab 1`` the second tab, and ``focus_tab title:logs`` will focus the
+    tab whose title matches "logs". See :ref:`search_syntax` for the full syntax
+    of match expressions. This is useful for session files that create multiple
+    tabs and want to ensure a specific tab is active when the session is loaded.
 
 ``enabled_layouts comma separated list of layout names``
     Set the layouts allowed in the current tab. Same syntax as