chore: snapshot working tree - pty_exited notifications + in-flight inference WIP

feat(booterm): structured pty_exited WS notifications. Plan-validated, impl-validated, code-reviewed green (contracts build clean, contracts test 29/29, booterm + web typecheck clean).

wip: in-progress inference/provider refactor (agents.ts, provider.ts, new llama-providers.ts, removed llama-args-validator), plus arena, dispatcher, compaction, schema changes.

openspec: pty-exit-notifications complete; x-agent-flags planned (not yet implemented).

packages/contracts/package.json

@@ -32,6 +32,10 @@
     "./arena": {
       "types": "./dist/arena.d.ts",
       "default": "./dist/arena.js"
+    },
+    "./llama-providers": {
+      "types": "./dist/llama-providers.d.ts",
+      "default": "./dist/llama-providers.js"
     }
   },
   "scripts": {