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.

README.md

@@ -31,8 +31,10 @@ python3 tests/smoke_test.py   # library self-test
 python3 tools/make_tune.py tunes/specs/04_tea_break_at_the_terminal.json --render
 ```
 
-Rendering needs `timidity` + a GM soundfont (`FluidR3_GM.sf2`). Note:
-Debian's timidity build has no `-O2` mode — use `-Ow -s 44`.
+Rendering needs `timidity` + a GM soundfont (`FluidR3_GM.sf2`, MIT —
+`apt install fluid-soundfont-gm`), or skip soundfonts entirely and render
+through OPL3 emulation — see [OPL3 rendering](#opl3-rendering-the-authentic-one).
+Note: Debian's timidity build has no `-O2` mode — use `-Ow -s 44`.
 
 **AI agents**: see [AGENTS.md](AGENTS.md) — the JSON spec format is the
 agent-friendly front door; no Python required to make a tune.

tunes/01_service_station_2am.py

@@ -137,6 +137,7 @@ def build():
 
 
 if __name__ == "__main__":
+    os.makedirs(os.path.dirname(OUT), exist_ok=True)
     mf = build()
     mf.write(OUT)
     d = verify(OUT, min_sec=40, max_sec=120)

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)

tunes/03_late_equaliser.py

@@ -133,6 +133,7 @@ def build():
 
 
 if __name__ == "__main__":
+    os.makedirs(os.path.dirname(OUT), exist_ok=True)
     mf = build()
     mf.write(OUT)
     dd = verify(OUT, min_sec=30, max_sec=120)