Split crates/config/src/lib.rs (1441 lines) into engine/

Pure reorganization, no behavior change - verified by diffing the
function-name and struct/enum-name sets before/after (both identical)
plus a full cargo test pass. lib.rs is now a thin shim (mod
declarations + pub use) since a crate root can't itself become a
directory; all the actual content moved into engine/, split along the
Lua API's own srd.*/srd.window.*/srd.layout.*/srd.workspace.*/
srd.theme.* namespace groupings the file's own section comments
already used:

- mod.rs: SharedState, Engine, ConfigError, and Engine's core methods
  (new/get/set/dispatch/reload/...).
- register.rs: register_srd_module, which wires every fn_* builder
  from every other file into the srd Lua table - the one place that
  genuinely needs to see all of them.
- general.rs/window.rs/layout.rs/workspace.rs/theme.rs: the fn_*
  builder methods themselves, one file per srd.* sub-namespace.
- support.rs: free functions shared across those (do_reload,
  parse_direction, flatten_table_into, validate, default_config) and
  the WindowAction enum.
- tests.rs: the ~300-line test module, left unsplit for the same
  shared-helper reason manager/tests.rs and udev's tests were.

~40 fn_* methods and the support.rs free functions/enum went from
private to pub(super): called across what are now sibling submodules,
which Rust's privacy model doesn't let see each other's private items.

1 files changed, 32 insertions, 0 deletions

diff --git a/crates/config/src/engine/layout.rs b/crates/config/src/engine/layout.rs
new file mode 100644
index 0000000..ebdb317
--- /dev/null
+++ b/crates/config/src/engine/layout.rs
@@ -0,0 +1,32 @@
+use super::*;
+use super::support::flatten_table_into;
+
+impl Engine {
+    // ---- srd.layout.* ------------------------------------------------------
+
+    pub(super) fn fn_layout_set(&self) -> Result<mlua::Function<'_>> {
+        let state = self.state.clone();
+        Ok(self.lua.create_function(move |_, name: String| {
+            let wm = state.borrow().wm.clone();
+            let mut wm = wm.borrow_mut();
+            let ws = wm.current_workspace();
+            wm.set_layout(ws, name);
+            wm.arrange_workspace(ws);
+            Ok(())
+        })?)
+    }
+
+    pub(super) fn fn_layout_configure(&self) -> Result<mlua::Function<'_>> {
+        let state = self.state.clone();
+        Ok(self.lua.create_function(move |_, (name, table): (String, Table)| {
+            let mut s = state.borrow_mut();
+            flatten_table_into(&format!("layout.{name}"), &table, &mut s.values)?;
+            let master_ratio = s.values.get(&format!("layout.{name}.master_ratio")).and_then(|v| v.as_f64());
+            drop(s);
+            if let Some(ratio) = master_ratio {
+                state.borrow().wm.borrow_mut().tiling.master_ratio = ratio as f32;
+            }
+            Ok(())
+        })?)
+    }
+}