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.

0 files changed, 0 insertions, 0 deletions