feat(FN-2709): migrate Hermes runtime plugin to pi-ai streaming client

- Replace Hermes pi module integration with pi-ai session streaming and updated runtime adapter contracts
- Remove legacy engine guard scaffolding and add hermes-stream-client coverage for streaming behavior
- Rewrite plugin and engine e2e tests to align with the new runtime flow and regenerate dist artifacts
- Update Hermes runtime README and package metadata to document pi-ai execution expectations

plugins/fusion-plugin-hermes-runtime/package.json

@@ -21,8 +21,8 @@
     "test": "vitest run --silent=passed-only --reporter=dot"
   },
   "dependencies": {
-    "@fusion/engine": "workspace:*",
-    "@fusion/plugin-sdk": "workspace:*"
+    "@fusion/plugin-sdk": "workspace:*",
+    "@mariozechner/pi-ai": "^0.70.0"
   },
   "devDependencies": {
     "@types/node": "^25.5.2",