feat(core): event bus seed - envelope schema, durable topic log, OELBR kernel

- EventBus: dumb wire, publish/subscribe, failures surface
- Envelope: four schema planes, inject-only headers, content-addressed
- TopicLog: owned SQLite ledger, replay + by-type/time/causality
- Seed facade: durable=ledger+wire, ephemeral=wire only, fold-for-state
- Rung 1 kernel: OELBR loop, DAG plans, durable cancellation tokens
- Neuron v0 executable spec source; specs/event-bus.md citizen zero
- Standing orders: design-before-code doctrine installed

.gitignore

@@ -32,3 +32,5 @@ UPCOMING_CHANGELOG.md
 logs/
 *.bun-build
 tsconfig.tsbuildinfo
+runs/neuron-v0/universe.db*
+runs/rung1/universe.db*