rename crates/ to engrams/; add el-compiler el package with bootstrap artifact

- crates/ → engrams/ (Rust engrams live here)
- el-compiler/ added: el self-hosting compiler as an el package
  - src/{compiler,lexer,parser,codegen}.el
  - bootstrap/el-compiler.elc (114KB, Rust-compiled seed)
- el.toml Cargo.toml workspace paths updated
- neuron-rs cross-repo path deps fixed (were pointing to products/ instead of foundation/)

engrams/el-stdlib/src/math.rs

@@ -0,0 +1,49 @@
+//! Math operations: abs, max, min, floor, ceil, pow, sqrt, clamp.
+
+use el_types::{Type, TypeEnv};
+use super::fn_type;
+
+pub fn register(env: &mut TypeEnv) {
+    env.register_fn("math_abs",   fn_type(vec![Type::Float], Type::Float));
+    env.register_fn("math_max",   fn_type(vec![Type::Float, Type::Float], Type::Float));
+    env.register_fn("math_min",   fn_type(vec![Type::Float, Type::Float], Type::Float));
+    env.register_fn("math_floor", fn_type(vec![Type::Float], Type::Int));
+    env.register_fn("math_ceil",  fn_type(vec![Type::Float], Type::Int));
+    env.register_fn("math_round", fn_type(vec![Type::Float], Type::Int));
+    env.register_fn("math_pow",   fn_type(vec![Type::Float, Type::Float], Type::Float));
+    env.register_fn("math_sqrt",  fn_type(vec![Type::Float], Type::Float));
+    env.register_fn("math_clamp", fn_type(vec![Type::Float, Type::Float, Type::Float], Type::Float));
+    env.register_fn("math_abs_int", fn_type(vec![Type::Int], Type::Int));
+    env.register_fn("math_max_int", fn_type(vec![Type::Int, Type::Int], Type::Int));
+    env.register_fn("math_min_int", fn_type(vec![Type::Int, Type::Int], Type::Int));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn env() -> TypeEnv {
+        let mut e = TypeEnv::with_builtins();
+        register(&mut e);
+        e
+    }
+
+    #[test]
+    fn test_math_abs_registered() {
+        assert!(env().lookup_fn("math_abs").is_some());
+    }
+
+    #[test]
+    fn test_math_sqrt_returns_float() {
+        let e = env();
+        let ty = e.lookup_fn("math_sqrt").unwrap();
+        assert!(matches!(ty, Type::Fn { return_type, .. } if matches!(return_type.as_ref(), Type::Float)));
+    }
+
+    #[test]
+    fn test_math_floor_returns_int() {
+        let e = env();
+        let ty = e.lookup_fn("math_floor").unwrap();
+        assert!(matches!(ty, Type::Fn { return_type, .. } if matches!(return_type.as_ref(), Type::Int)));
+    }
+}