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/)

neuron-lang/health.el

@@ -0,0 +1,13 @@
+// health.el — Health check and status handlers.
+
+fn health_response() -> String {
+    let mode: String = state_get("neuron_mode")
+    if str_eq(mode, "") {
+        return "{\"status\":\"ok\",\"version\":\"1.0.0-engram\"}"
+    }
+    return "{\"status\":\"ok\",\"version\":\"1.0.0-engram\",\"mode\":\"" + mode + "\"}"
+}
+
+fn not_found_response(path: String) -> String {
+    return "{\"error\":\"not found\",\"path\":\"" + path + "\"}"
+}