Add synthetic sample library

docs/design/sample-library.md

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+# Synthetic Sample Library
+
+## Problem
+
+Real Serato libraries contain private paths, listening history, and copyrighted
+music. Contributors still need a repeatable library for tests and demonstrations.
+
+## Architecture
+
+`samples/small-library/manifest.json` describes a compact migration scenario.
+`generate.py` turns that manifest into fake audio files and UTF-16-LE crate files
+inside an ignored `generated` directory. The generated files are disposable and
+contain no real audio or user library data.
+
+## Edge Cases
+
+- Five manually maintained crates and two smart/dynamic crates.
+- Mixed supported audio extensions.
+- One reference whose file is absent.
+- One stale reference whose file has been renamed.
+- References shared by static and smart crates.
+
+## Verification
+
+`pytest` generates the sample in a temporary directory and verifies its crate,
+track, and missing-reference counts through the production parser and scanner.