feat(neuron): rung-zero live - first conversation on pure-Neuron stack

- kernel/graph: nodes+edges append-only store
- conversation: chained turns, memory node, fold-based reads
- session/sessions: durable admission inbox, promotion, serialized runner,
  eager tool settlement, provider/dialect/transform injected at composition
- provider/dialects: raw-wire anthropic + openai-compatible, registry
- llm/stream, tools(bash/read/write), auth(local claims), boot composition
- providers resolve from ~/.config/neuron/providers.json - no baked vendors

nix/opencode.nix

@@ -52,7 +52,7 @@ stdenvNoCC.mkDerivation (finalAttrs: {
   buildPhase = ''
     runHook preBuild
 
-    cd ./packages/opencode
+    cd ./packages/neuron
     bun --bun ./script/build.ts --single --skip-install
     bun --bun ./script/schema.ts schema.json