feat: @agor/stores package + Electrobun hardening (WIP)

- packages/stores/: theme, notifications, health stores extracted
- Electrobun hardening: durable event sequencing, file conflict detection,
  push-based updates, backpressure guards (partial, agents still running)

packages/stores/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "@agor/stores",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module",
+  "main": "index.ts",
+  "types": "index.ts",
+  "exports": {
+    ".": "./index.ts",
+    "./*": "./*.ts"
+  },
+  "files": ["*.ts"]
+}