Restore upstream attribution in NOTICE (Qwen3-8B)

The shipped NOTICE reads "Copyright 2025-2026 Zen Authors" and names no upstream, but these weights are a derivative of Qwen/Qwen3-8B (Apache-2.0).

Apache-2.0 section 4(c) requires retaining upstream attribution notices in distributed derivative works; section 4(d) requires carrying upstream's NOTICE text where upstream ships one. Replacing upstream's copyright with Zen's drops both.

Evidence of derivation: via zenlm/zen-pro; config.json: Qwen3ForCausalLM, hidden 4096, 36 layers

This PR names the upstream and its true license, and keeps Zen's copyright scoped to Zen's own modifications. One LICENSE + one NOTICE; no license change.

NOTICE

@@ -1,5 +1,8 @@
-Zen
+zen-sql
 Copyright 2025-2026 Zen Authors
 
-This model and its accompanying code are licensed under the Apache License, Version 2.0.
-Zen models are developed by the Zen Authors (https://zenlm.org).
+This model is a derivative work distributed under the Apache-2.0 license.
+A copy of the license is in the accompanying LICENSE file.
+
+Built on:
+- Qwen3-8B (https://huggingface.co/Qwen/Qwen3-8B), Apache-2.0.