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, 6 insertions, 2 deletions

diff --git a/crates/config/src/engine/general.rs b/crates/config/src/engine/general.rs
index c8a136f..68b441e 100644
--- a/crates/config/src/engine/general.rs
+++ b/crates/config/src/engine/general.rs
@@ -109,7 +109,7 @@ impl Engine {
 
     pub(super) fn fn_bind(&self) -> Result<mlua::Function<'_>> {
         let state = self.state.clone();
-        Ok(self.lua.create_function(move |lua, (combo, f): (String, mlua::Function)| {
+        Ok(self.lua.create_function(move |lua, (combo, f, description): (String, mlua::Function, Option<String>)| {
             // `key_bindings` is keyed by whatever string dispatch builds
             // from a real keypress (`srdwm_core::key_combo_string`, fixed
             // Ctrl/Shift/Alt/Mod4 order) - storing the config's own
@@ -119,7 +119,11 @@ impl Engine {
             // grabbed/intercepted. See `parse_key_combo`'s doc comment.
             let combo = srdwm_core::canonicalize_key_combo(&combo);
             let key = lua.create_registry_value(f)?;
-            state.borrow_mut().key_bindings.insert(combo, key);
+            let mut s = state.borrow_mut();
+            if let Some(description) = description.filter(|d| !d.trim().is_empty()) {
+                s.key_descriptions.insert(combo.clone(), description);
+            }
+            s.key_bindings.insert(combo, key);
             Ok(())
         })?)
     }