docs: add README.md for vite_task crate (#245)

Author: branchseer

crates/vite_task/README.md

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+# vite_task
+
+This is the top-level library crate that orchestrates the full task lifecycle: loading the task graph, planning execution, running or replaying tasks , and reporting results.
+
+It is consumed by two binaries:
+
+- **[Vite+](https://github.com/voidzero-dev/vite-plus)** — the official product, where it powers `vp run`
+- **[`vite_task_bin`](../vite_task_bin)** — internal `vt` CLI for developing and testing this repo without the full Vite+ stack