Make wlgrid a chooser only, and say what each format is

--focus and sway::focus are gone. Showing the grid and reporting the
choice is the whole job; deciding what the choice means belongs to
whoever called it, and keeping that decision here only invited more of
it (focus which way? move? swap? scratchpad?). The sway IPC connection
is now scoped to building the list and closed before the overlay maps.

--help no longer just names the three formats, it shows them. Each gets
a real sample line, what every column means, and where the format is
meant to be used: tsv for `IFS=$'\t' read` or cut, json for jq, portal
for xdg-desktop-portal-wlr's simple chooser, with the config stanza to
paste. Plus worked examples of focusing a window, handling either kind
of pick, and screenshotting one with grim -T.

src/sway.rs

@@ -1,7 +1,9 @@
-//! sway stays the source of truth for the window list and for focusing, exactly
-//! as the shell script this replaces did (`swaymsg -t get_tree` + `[con_id=N]
-//! focus`). The Wayland side only supplies pixels; the join between the two is
+//! sway is the source of truth for the window list (`swaymsg -t get_tree`); the
+//! Wayland side only supplies pixels. The join between the two is
 //! `foreign_toplevel_identifier`, which sway reports per view.
+//!
+//! Acting on the choice is deliberately not here: wlgrid reports what was picked
+//! and the caller decides what that means.
 
 use swayipc::{Connection, Node, NodeType};
 
@@ -47,15 +49,3 @@ pub fn scale(conn: &mut Connection) -> Result<i32, swayipc::Error> {
         .unwrap_or(1)
         .max(1))
 }
-
-pub fn focus(conn: &mut Connection, target: &Target) -> Result<(), swayipc::Error> {
-    let cmd = match target.con_id {
-        Some(con_id) => format!("[con_id={con_id}] focus"),
-        // Picking a display means going to it.
-        None => format!("focus output {}", target.id),
-    };
-    for res in conn.run_command(cmd)? {
-        res?;
-    }
-    Ok(())
-}