fix cross-repo path deps; remove el compiler from neuron-lang/

- neuron-runtime, neuron-store, neuron-migrate: fix path deps
  (products/engram/ → foundation/engram/engrams/, products/el/ → foundation/el/engrams/)
- neuron-rs workspace: fix axon-events/axon-protocol paths
  (../../../platform/ → ../../platform/, paths were off by one level)
- neuron-lang/compiler/ removed (el self-hosting compiler now lives in foundation/el/el-compiler/)

crates/neuron-protocol/Cargo.toml

@@ -2,18 +2,20 @@
 name = "neuron-protocol"
 version = "0.1.0"
 edition = "2021"
+description = "Thin re-export shim — delegates to the canonical axon-protocol and axon-events platform crates."
 
 [dependencies]
+# Canonical platform crates — all real types live here
+axon-protocol = { workspace = true }
+axon-events = { workspace = true }
+
+# Retained for any neuron-rs–specific protocol extensions
 neuron-domain = { path = "../neuron-domain" }
-neuron-store = { path = "../neuron-store" }
-axon-events = { path = "../axon-events" }
 serde = { workspace = true }
 serde_json = { workspace = true }
 uuid = { workspace = true }
 tokio = { workspace = true }
-axum = { workspace = true }
 tracing = { workspace = true }
 thiserror = { workspace = true }
 
 [dev-dependencies]
-tempfile = "3"