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/)

el-compiler/el.toml

@@ -0,0 +1,8 @@
+[package]
+name = "el-compiler"
+version = "0.1.0"
+description = "el self-hosting compiler — lexer, parser, codegen"
+edition = "2026"
+
+[build]
+entry = "src/compiler.el"