Round-off: README render routes, tune scripts create midi/ if missing

Fresh-clone test passes end-to-end: clone -> build_all.sh -> all four
tunes generate, verify, render and pass audio checks with no prior state.

tunes/02_kestrel_over_the_fens.py

@@ -109,6 +109,7 @@ def build():
 
 
 if __name__ == "__main__":
+    os.makedirs(os.path.dirname(OUT), exist_ok=True)
     mf = build()
     mf.write(OUT)
     d = verify(OUT, min_sec=50, max_sec=150)