Expose key bindings over IPC so a launcher can list them

Asked whether srdwm's bindings show in the AGS launcher. They could not:
srd.bind lives entirely in the Lua engine, and nothing published a binding
anywhere a client could read it. There was no IPC command, no field in any
response, and bound_keys() was used only by main.rs to register grabs.

srd.bind now takes an optional third argument, a description, and the loaded
set is copied into the WindowManager after the initial load and after every
reload. Core neither owns nor interprets them - it has no Lua state and
never dispatches a key - it holds them so the IPC layer, which is handed a
WindowManager and nothing else, can serve them. New `srd keybindings` returns
combo and description pairs, sorted so a UI listing them does not reshuffle
on every refresh.

Every binding in the shipped config now carries a description, so the feature
is useful without the user writing any.

Verified live in a nested instance: 46 bindings published, 0 without a
description, and editing the config file updated the list without a restart
(which also exercised reload-on-write again).

Also verified, for the separate report that windows cannot be moved to
another workspace from the AGS workspace pills: the compositor side works.
`srd dispatch move workspace <id> 2` moved a window from workspace 1 to 2 and
correctly hid it, since workspace 1 was active. Nothing to fix here; the
missing piece is on the shell side.

515 tests pass, clippy clean.

1 files changed, 3 insertions, 1 deletions

diff --git a/crates/config/src/engine/support.rs b/crates/config/src/engine/support.rs
index 76bcf5e..9d81035 100644
--- a/crates/config/src/engine/support.rs
+++ b/crates/config/src/engine/support.rs
@@ -33,16 +33,18 @@ pub(super) fn do_reload(lua: &Lua, state: &Rc<RefCell<SharedState>>) -> Result<(
             std::mem::take(&mut s.key_bindings),
             std::mem::take(&mut s.event_handlers),
             std::mem::take(&mut s.repeat_keys),
+            std::mem::take(&mut s.key_descriptions),
         );
         (s.config_dir.clone(), previous)
     };
-    let restore = |state: &Rc<RefCell<SharedState>>, previous: (_, _, _)| {
+    let restore = |state: &Rc<RefCell<SharedState>>, previous: (_, _, _, _)| {
         let mut s = state.borrow_mut();
         // Whatever the failed run managed to register before erroring is
         // discarded, not merged: half of a broken config is not a config.
         s.key_bindings = previous.0;
         s.event_handlers = previous.1;
         s.repeat_keys = previous.2;
+        s.key_descriptions = previous.3;
     };
     let path = config_dir.join("init.lua");
     let src = match std::fs::read_to_string(&path) {