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.

README.md

@@ -1,7 +1,7 @@
 # wlgrid
 
 A window switcher for wlroots compositors: a grid overlay of **live** window
-previews that looks like a rofi theme, and focuses the window you pick.
+previews that looks like a rofi theme, and tells you which one you picked.
 
 It replaces a `wlthumbs | rofi` pipeline, and doubles as a screencast source
 picker for the desktop portal. The difference is that no thumbnails
@@ -39,7 +39,6 @@ wlgrid [--print] [--verbose] [--hide-labels] [--font FAMILY] [--font-size PX]
        [--live all|current|none] [--fps N] [--timeout SECS]
 ```
 
-- `--print` writes the selected sway `con_id` to stdout instead of focusing it
 - `--verbose` prints phase timings and how many windows were captured
 - `--hide-labels` draws an icon-only grid
 - `--font FAMILY` label font family (default `Berkeley Mono`)
@@ -53,14 +52,12 @@ wlgrid is a chooser: it reports what you picked and leaves acting on it to the
 caller. The pick goes to stdout, nothing does if you cancel, and the exit status
 is 0 for a pick and 1 for a cancel.
 
+wlgrid never acts on the choice — it has no idea what you want to do with it.
+Focusing on sway looks like this:
+
 ```sh
-# Simplest: let wlgrid do the focusing, for a bare keybinding.
-bindsym $mod+Tab exec wlgrid --focus
-
-# Windows only, in a script:
-swaymsg "[con_id=$(wlgrid --no-outputs | cut -f2)] focus"
-
-# Both windows and displays: the TYPE column says which command to use.
+#!/usr/bin/env bash
+# ~/.local/bin/winmenu, bound to $mod+Tab
 IFS=$'\t' read -r type id toplevel app title < <(wlgrid) || exit 0
 case $type in
     window) swaymsg "[con_id=$id] focus" ;;
@@ -68,8 +65,11 @@ case $type in
 esac
 ```
 
-`--focus` runs exactly those two commands for you. (Focusing a display only does
-something visible when you have more than one.)
+Windows only, as a one-liner:
+
+```sh
+swaymsg "[con_id=$(wlgrid --no-outputs | cut -f2)] focus"
+```
 
 Three formats, because the identifiers different consumers need differ:
 
@@ -145,8 +145,9 @@ A wlroots compositor advertising `ext-image-copy-capture-v1`,
 `ext-image-capture-source-v1` (with the foreign-toplevel source manager),
 `ext-foreign-toplevel-list-v1`, `wlr-layer-shell-unstable-v1` and
 `wp_viewporter` — sway 1.11+, and in principle Hyprland, labwc and jay, though
-only sway is tested. sway is also the source of truth for the window list and
-for focusing, over its IPC socket.
+only sway is tested. sway is also the source of truth for the window list, over
+its IPC socket, which is the one thing that would need replacing to run
+elsewhere (`ext-foreign-toplevel-list-v1` already reports app id and title).
 
 Known upstream issue: holding per-toplevel capture sessions open makes windows
 blurry on **fractionally scaled** outputs