feat: DSML tool-call recovery plugin for OpenCode V2

Recovers DeepSeek DSML tool calls that leak as assistant text: streaming
middleware (AI-SDK path), SSE rewrite (native path), history sanitization,
preventive directive, conditional system nudge, and a capped idle watchdog.
116 tests, synthetic golden fixtures.

server.ts

@@ -0,0 +1,5 @@
+/**
+ * Plugin server entrypoint (resolved by OpenCode's local-directory loader).
+ * Implementation lives in `src/`.
+ */
+export { default } from "./src/index.ts"