feat: Implement senior audio injection with 5 fallback methods

- Add _cmd_create_arrangement_audio_pattern with 5-method fallback chain
- Method 1: track.insert_arrangement_clip() [Live 12+]
- Method 2: track.create_audio_clip() [Live 11+]
- Method 3: arrangement_clips.add_new_clip() [Live 12+]
- Method 4: Session->duplicate_clip_to_arrangement [Legacy]
- Method 5: Session->Recording [Universal]

- Add _cmd_duplicate_clip_to_arrangement for session-to-arrangement workflow
- Update skills documentation
- Verified: 3 clips created at positions [0, 4, 8] in Arrangement View

Closes: Audio injection in Arrangement View

mcp_server/engines/musical_intelligence.py

@@ -0,0 +1,29 @@
+"""Small compatibility layer for legacy musical_intelligence imports."""
+
+from typing import Any, Dict, List
+
+
+class MusicalIntelligenceEngine:
+    """Expose only the legacy methods still imported by server.py."""
+
+    def __init__(self):
+        self._progressions: List[Dict[str, Any]] = []
+        self._current_key = "Am"
+
+    def set_multiple_progressions(self, progressions_config: List[Dict[str, Any]]) -> Dict[str, Any]:
+        self._progressions = list(progressions_config or [])
+        return {
+            "sections": [item.get("section", "") for item in self._progressions],
+            "progressions": [item.get("progression", "") for item in self._progressions],
+            "total_chords": sum(len(str(item.get("progression", "")).split("-")) for item in self._progressions),
+        }
+
+    def modulate_key(self, section_index: int, new_key: str) -> Dict[str, Any]:
+        original_key = self._current_key
+        self._current_key = new_key
+        return {
+            "original_key": original_key,
+            "new_key": new_key,
+            "modulation_type": "direct",
+            "tracks_affected": [section_index],
+        }