Fix solo string instruments: clean triangle, no detune

Solo violin/viola/cello/contrabass now use triangle + strings envelope
(clean, clear). String ensemble keeps strings_synth + detune for
thick ensemble textures. Solo instruments need clarity, not width.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pytheory/rhythm.py

@@ -45,28 +45,28 @@ INSTRUMENTS = {
 
     # ── Strings ──
     "violin": {
-        "synth": "strings_synth", "envelope": "strings",
-        "detune": 4, "lowpass": 5000,
+        "synth": "triangle", "envelope": "strings",
+        "lowpass": 5000,
         "humanize": 0.15,
     },
     "viola": {
-        "synth": "strings_synth", "envelope": "strings",
-        "detune": 4, "lowpass": 3500,
+        "synth": "triangle", "envelope": "strings",
+        "lowpass": 3500,
         "humanize": 0.15,
     },
     "cello": {
-        "synth": "strings_synth", "envelope": "strings",
-        "detune": 4, "lowpass": 2500,
+        "synth": "triangle", "envelope": "strings",
+        "lowpass": 2500,
         "humanize": 0.15,
     },
     "contrabass": {
-        "synth": "strings_synth", "envelope": "strings",
-        "detune": 3, "lowpass": 1500,
+        "synth": "triangle", "envelope": "strings",
+        "lowpass": 1500,
         "humanize": 0.1,
     },
     "string_ensemble": {
         "synth": "strings_synth", "envelope": "pad",
-        "detune": 12, "spread": 0.6,
+        "detune": 10, "spread": 0.5,
         "chorus": 0.2, "chorus_rate": 0.5,
         "lowpass": 4000,
     },

test_pytheory.py

@@ -6470,7 +6470,7 @@ def test_instrument_violin():
     from pytheory import Score
     score = Score("4/4", bpm=120)
     p = score.part("v", instrument="violin")
-    assert p.synth == "strings_synth"
+    assert p.synth == "triangle"
     assert p.envelope == "strings"
     assert p.humanize == 0.15
     assert p.lowpass == 5000