feat: AI Copilot suggestion chips + typeahead dropdown

- Suggestion chips bar: context-aware (amber for rearrange, indigo for creation)
- Typeahead dropdown: keyword matching on ≥2 chars, Tab to select
- getSelectedMidiItemInfo helper for context detection
- Backend: 4 rearrange presets in ai_presets.py
- PromptTemplateManager: getContextualSuggestions(hasSelectedItem)

app/api/v1/ai_presets.py

@@ -48,6 +48,58 @@ DEFAULT_PRESETS = [
         "is_user_defined": False,
         "is_favorite": False,
         "created_at": "2026-07-23T16:00:00Z"
+    },
+    {
+        "id": "preset_rearrange_jazz_swing",
+        "name": "Jazz Swing Variation",
+        "keywords": ["jazz", "swing", "rearrange to jazz", "jazz improv"],
+        "category": "Rearrange / Variation",
+        "default_bars": 4,
+        "default_bpm": 120,
+        "default_scale": "C Major",
+        "system_instruction_template": "Rearrange the original melody into a rhythmic Jazz Swing style. Apply syncopation, 7th/9th chord extensions, and off-beat rhythmic feel.",
+        "is_user_defined": False,
+        "is_favorite": True,
+        "created_at": "2026-07-28T11:00:00Z"
+    },
+    {
+        "id": "preset_rearrange_synth_arpeggio",
+        "name": "80s Synthwave Arpeggiator",
+        "keywords": ["synthwave", "arpeggio", "arp", "16th variation", "80s synth"],
+        "category": "Rearrange / Variation",
+        "default_bars": 4,
+        "default_bpm": 120,
+        "default_scale": "C Minor",
+        "system_instruction_template": "Transform this sequence into a driving, shimmering 16th-note Arpeggio string in classic 80s Synthwave/Trance style.",
+        "is_user_defined": False,
+        "is_favorite": False,
+        "created_at": "2026-07-28T11:00:00Z"
+    },
+    {
+        "id": "preset_rearrange_harmonize",
+        "name": "Chords Harmonization (4-Note)",
+        "keywords": ["harmonize", "harmony", "add chord notes", "rich melody"],
+        "category": "Rearrange / Variation",
+        "default_bars": 4,
+        "default_bpm": 120,
+        "default_scale": "C Major",
+        "system_instruction_template": "Add harmonizing notes to create lush 4-note chord voicing extensions beneath the lead melody.",
+        "is_user_defined": False,
+        "is_favorite": False,
+        "created_at": "2026-07-28T11:00:00Z"
+    },
+    {
+        "id": "preset_rearrange_cinematic_strings",
+        "name": "Cinematic Strings Staccato",
+        "keywords": ["cinematic", "strings", "staccato", "staccato strings"],
+        "category": "Rearrange / Variation",
+        "default_bars": 4,
+        "default_bpm": 120,
+        "default_scale": "C Minor",
+        "system_instruction_template": "Rearrange the original line into a dramatic, driving Staccato rhythm for a Strings Ensemble.",
+        "is_user_defined": False,
+        "is_favorite": True,
+        "created_at": "2026-07-28T11:00:00Z"
     }
 ]