refactor: remove runtime invariant plugins

Delete @deepseek-ai/dsh-invariants, every package's ./invariant companion
and its tests, the invariant gates and Vitest setup, the scoped-event
resolver generator, and the INVARIANT-coded listener rethrow paths.
Update docs, READMEs, Agent Notes, and add an upgrade guide.

python/sdk-runtime/package.json

@@ -57,7 +57,6 @@
     "@deepseek-ai/dsh-host-plugin-inventory": "workspace:*",
     "@deepseek-ai/dsh-host-webserver": "workspace:*",
     "@deepseek-ai/dsh-http-proxy": "workspace:*",
-    "@deepseek-ai/dsh-invariants": "workspace:*",
     "@deepseek-ai/dsh-jobs": "workspace:*",
     "@deepseek-ai/dsh-jobs-local": "workspace:*",
     "@deepseek-ai/dsh-launch-environment": "workspace:*",