feat: Enhance musician API with cross-band sit-in tracking

- Add sit_in_summary to GET /musicians/{slug}
- Add stats: total_bands, current_bands, total_sit_ins
- Include song_title, show_date, vertical in guest appearances
- Add seed_musicians.py for initial musician data

backend/routers/musicians.py

@@ -60,6 +60,8 @@ def list_musicians(
 @router.get("/{slug}")
 def get_musician(slug: str, session: Session = Depends(get_session)):
     """Get musician details with band memberships and guest appearances"""
+    from models import Show, Song, Vertical
+    
     musician = session.exec(select(Musician).where(Musician.slug == slug)).first()
     if not musician:
         raise HTTPException(status_code=404, detail="Musician not found")
@@ -70,8 +72,10 @@ def get_musician(slug: str, session: Session = Depends(get_session)):
     ).all()
     
     bands = []
+    primary_band_ids = set()
     for m in memberships:
         artist = session.get(Artist, m.artist_id)
+        primary_band_ids.add(m.artist_id)
         bands.append({
             "id": m.id,
             "artist_id": m.artist_id,
@@ -80,20 +84,44 @@ def get_musician(slug: str, session: Session = Depends(get_session)):
             "role": m.role,
             "start_date": str(m.start_date) if m.start_date else None,
             "end_date": str(m.end_date) if m.end_date else None,
+            "is_current": m.end_date is None,
         })
     
-    # Get guest appearances
+    # Get guest appearances with full context
     appearances = session.exec(
         select(PerformanceGuest).where(PerformanceGuest.musician_id == musician.id)
     ).all()
     
     guests = []
+    sit_in_verticals = {}  # Track which bands they've sat in with
+    
     for g in appearances:
         perf = session.get(Performance, g.performance_id)
+        if not perf:
+            continue
+            
+        show = session.get(Show, perf.show_id) if perf else None
+        song = session.get(Song, perf.song_id) if perf else None
+        vertical = session.get(Vertical, show.vertical_id) if show else None
+        
+        if vertical:
+            if vertical.id not in sit_in_verticals:
+                sit_in_verticals[vertical.id] = {
+                    "vertical_id": vertical.id,
+                    "vertical_name": vertical.name,
+                    "vertical_slug": vertical.slug,
+                    "count": 0
+                }
+            sit_in_verticals[vertical.id]["count"] += 1
+        
         guests.append({
             "id": g.id,
             "performance_id": g.performance_id,
             "performance_slug": perf.slug if perf else None,
+            "song_title": song.title if song else None,
+            "show_date": str(show.date.date()) if show and show.date else None,
+            "vertical_name": vertical.name if vertical else None,
+            "vertical_slug": vertical.slug if vertical else None,
             "instrument": g.instrument,
         })
     
@@ -108,6 +136,13 @@ def get_musician(slug: str, session: Session = Depends(get_session)):
         },
         "bands": bands,
         "guest_appearances": guests,
+        "sit_in_summary": list(sit_in_verticals.values()),
+        "stats": {
+            "total_bands": len(bands),
+            "current_bands": len([b for b in bands if b.get("is_current")]),
+            "total_sit_ins": len(guests),
+            "bands_sat_in_with": len(sit_in_verticals),
+        }
     }
 
 # --- Admin Endpoints (for now, no auth check - can be added later) ---

backend/seed_musicians.py

@@ -0,0 +1,116 @@
+"""
+Seed script to create common cross-band musicians.
+
+These are musicians known for sitting in with multiple bands.
+"""
+
+from sqlmodel import Session, select
+from database import engine
+from models import Musician, Artist, BandMembership
+import re
+
+
+def generate_slug(name: str) -> str:
+    """Generate URL-safe slug"""
+    slug = name.lower()
+    slug = re.sub(r'[^\w\s-]', '', slug)
+    slug = re.sub(r'[\s_]+', '-', slug)
+    return slug.strip('-')
+
+
+# Notable jam scene musicians who appear across bands
+CROSS_BAND_MUSICIANS = [
+    # Grateful Dead / Dead Family
+    {"name": "Bob Weir", "primary_instrument": "Guitar", "bands": ["grateful-dead", "dead-and-company"]},
+    {"name": "Mickey Hart", "primary_instrument": "Drums", "bands": ["grateful-dead", "dead-and-company"]},
+    {"name": "Bill Kreutzmann", "primary_instrument": "Drums", "bands": ["grateful-dead", "dead-and-company"]},
+    {"name": "John Mayer", "primary_instrument": "Guitar", "bands": ["dead-and-company"]},
+    {"name": "Oteil Burbridge", "primary_instrument": "Bass", "bands": ["dead-and-company"]},
+    {"name": "Jeff Chimenti", "primary_instrument": "Keyboards", "bands": ["dead-and-company"]},
+    
+    # Goose
+    {"name": "Rick Mitarotonda", "primary_instrument": "Guitar, Vocals", "bands": ["goose"]},
+    {"name": "Peter Anspach", "primary_instrument": "Keyboards, Guitar", "bands": ["goose"]},
+    {"name": "Trevor Weekz", "primary_instrument": "Bass", "bands": ["goose"]},
+    {"name": "Ben Atkind", "primary_instrument": "Drums", "bands": ["goose"]},
+    {"name": "Jeff Arevalo", "primary_instrument": "Percussion", "bands": ["goose"]},
+    
+    # Phish
+    {"name": "Trey Anastasio", "primary_instrument": "Guitar", "bands": ["phish"]},
+    {"name": "Page McConnell", "primary_instrument": "Keyboards", "bands": ["phish"]},
+    {"name": "Mike Gordon", "primary_instrument": "Bass", "bands": ["phish"]},
+    {"name": "Jon Fishman", "primary_instrument": "Drums", "bands": ["phish"]},
+    
+    # Billy Strings
+    {"name": "Billy Strings", "primary_instrument": "Guitar, Vocals", "bands": ["billy-strings"]},
+    {"name": "Billy Failing", "primary_instrument": "Banjo", "bands": ["billy-strings"]},
+    {"name": "Royal Masat", "primary_instrument": "Bass", "bands": ["billy-strings"]},
+    {"name": "Jarrod Walker", "primary_instrument": "Mandolin", "bands": ["billy-strings"]},
+    
+    # Cross-band sit-in regulars
+    {"name": "Marcus King", "primary_instrument": "Guitar, Vocals", "bands": []},
+    {"name": "Pigeons Playing Ping Pong", "primary_instrument": "Funk", "bands": []},
+    {"name": "Karina Rykman", "primary_instrument": "Bass, Vocals", "bands": []},
+]
+
+
+def seed_musicians():
+    """Create musicians if they don't exist"""
+    print("Seeding musicians...\n")
+    
+    with Session(engine) as session:
+        created = 0
+        
+        for m in CROSS_BAND_MUSICIANS:
+            slug = generate_slug(m["name"])
+            
+            existing = session.exec(
+                select(Musician).where(Musician.slug == slug)
+            ).first()
+            
+            if existing:
+                print(f"  Exists: {m['name']}")
+                musician = existing
+            else:
+                musician = Musician(
+                    name=m["name"],
+                    slug=slug,
+                    primary_instrument=m["primary_instrument"]
+                )
+                session.add(musician)
+                session.commit()
+                session.refresh(musician)
+                created += 1
+                print(f"  Created: {m['name']}")
+            
+            # Create band memberships
+            for band_slug in m.get("bands", []):
+                # Find vertical by slug to get artist
+                from models import Vertical
+                vertical = session.exec(
+                    select(Vertical).where(Vertical.slug == band_slug)
+                ).first()
+                
+                if vertical and vertical.primary_artist_id:
+                    # Check if membership exists
+                    existing_membership = session.exec(
+                        select(BandMembership)
+                        .where(BandMembership.musician_id == musician.id)
+                        .where(BandMembership.artist_id == vertical.primary_artist_id)
+                    ).first()
+                    
+                    if not existing_membership:
+                        membership = BandMembership(
+                            musician_id=musician.id,
+                            artist_id=vertical.primary_artist_id,
+                            role=m["primary_instrument"]
+                        )
+                        session.add(membership)
+                        print(f"    -> Added to {band_slug}")
+        
+        session.commit()
+        print(f"\nCreated {created} new musicians")
+
+
+if __name__ == "__main__":
+    seed_musicians()