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-build/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "el-build"
+description = "Build orchestrator and incremental build system for the Engram language toolchain"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[dependencies]
+el-manifest   = { path = "../el-manifest" }
+el-registry   = { path = "../el-registry" }
+el-compiler   = { path = "../el-compiler" }
+el-lexer      = { workspace = true }
+el-parser     = { workspace = true }
+el-types      = { workspace = true }
+el-seal       = { workspace = true }
+serde         = { workspace = true }
+serde_json    = { workspace = true }
+thiserror     = { workspace = true }
+blake3        = { workspace = true }
+tokio         = { version = "1", features = ["fs", "io-util", "rt", "macros", "process"] }
+semver        = { version = "1", features = ["serde"] }
+
+[dev-dependencies]
+tempfile      = "3"