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/neuron.el

@@ -0,0 +1,80 @@
+// neuron.el — Neuron intelligence entry point.
+//
+// This is the root module loaded by neuron-runtime at startup. It wires
+// all subsystems together and defines the swarm coordinator — the function
+// that handles every incoming tool call.
+//
+// Architecture intent:
+// Neuron is a swarm agent: one coordinator orchestrates multiple specialized
+// subsystems (memory, knowledge, backlog, context, artifact, etc.). Each
+// subsystem is a focused el module. The coordinator dispatches
+// to the right subsystem based on tool_name.
+//
+// The @swarm_coordinator decorator tells the engram runtime that this function
+// is the root entry point for the agent. The runtime calls handle_tool_call()
+// for every incoming Axon message.
+//
+// Startup sequence (enforced by the runtime):
+//   1. Load types.el         — graph schema registration
+//   2. Load all subsystems   — function registration
+//   3. Load axon.el          — dispatch table
+//   4. Load neuron.el        — entry point wiring
+//   5. Call version()        — runtime health check
+//
+// This file intentionally contains minimal logic. It's the composition
+// root, not a logic layer. Keep it thin.
+
+from axon import { dispatch_tool }
+from types import { NeuronError }
+
+// ── Swarm coordinator ─────────────────────────────────────────────────────────
+
+// handle_tool_call — the root entry point for all Axon tool invocations.
+//
+// The @swarm_coordinator decorator registers this function as the agent's
+// primary message handler. The runtime calls it for every incoming tool call
+// after authentication is verified at the protocol layer.
+//
+// It delegates entirely to dispatch_tool() in axon.el — the coordinator
+// should not contain routing logic.
+@swarm_coordinator
+fn handle_tool_call(
+    tool_name: String,
+    params: Map<String, String>,
+) -> Result<Map<String, String>, NeuronError> {
+    dispatch_tool(tool_name, params)
+}
+
+// ── Health and metadata ───────────────────────────────────────────────────────
+
+// version — return the current Neuron version string.
+//
+// @public — called by the runtime health check without authentication.
+// The format is "neuron/<version>-engram" to distinguish from the Kotlin
+// predecessor (which used "neuron/<version>-kotlin").
+@public
+fn version() -> String {
+    "neuron/1.0.0-engram"
+}
+
+// health — lightweight liveness probe.
+//
+// Returns "ok" if the engram runtime and all subsystems loaded correctly.
+// Called by the /health HTTP endpoint in neuron-api.
+@public
+fn health() -> String {
+    "ok"
+}
+
+// ── Session bootstrap ─────────────────────────────────────────────────────────
+
+// on_startup — called once when the runtime initializes.
+//
+// Emits a startup event so Axon subscribers know Neuron is ready.
+// Does NOT run begin_session() — that's the caller's responsibility.
+// The runtime calls on_startup() once; callers call begin_session() per session.
+@manager
+fn on_startup() -> Result<String, NeuronError> {
+    native_emit("neuron.started", {"version": "1.0.0-engram"})
+    Ok("neuron ready")
+}