refactor: rename pod crate to worker

crates/worker/README.md

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+# worker
+
+## Role
+
+`worker` turns an `llm-engine` Engine into a named runtime entity with manifest configuration, scoped tools, session persistence, protocol handling, and Worker metadata integration.
+
+## Boundaries
+
+Owns:
+
+- Worker lifecycle and socket protocol serving
+- Engine construction around a resolved Manifest
+- session-store and pod-store coordination
+- built-in tool registration under scope/policy
+- spawned-child orchestration hooks
+
+Does not own:
+
+- provider-specific wire formats (`provider` / `llm-engine` clients)
+- product CLI parsing (`yoi`)
+- TUI display authority (`tui`)
+- current-state storage schema outside Worker metadata (`pod-store`)
+
+## Design notes
+
+A Worker is runtime authority, not UI state. It should commit model-visible events through history/session paths and keep current Worker-name state in Worker metadata rather than in transient runtime files.
+
+## See also
+
+- [`../../docs/design/worker-session-state.md`](../../docs/design/worker-session-state.md)
+- [`../../docs/design/context-history.md`](../../docs/design/context-history.md)
+- [`../../docs/design/tool-permissions-scope.md`](../../docs/design/tool-permissions-scope.md)