feat(social): Add Reaction model, schema, and API endpoints

backend/models.py

@@ -279,3 +279,13 @@ class Notification(SQLModel, table=True):
     created_at: datetime = Field(default_factory=datetime.utcnow)
     
     user: User = Relationship(back_populates="notifications")
+
+class Reaction(SQLModel, table=True):
+    id: Optional[int] = Field(default=None, primary_key=True)
+    user_id: int = Field(foreign_key="user.id")
+    entity_type: str = Field(index=True) # "review", "comment"
+    entity_id: int = Field(index=True)
+    emoji: str # "❤️", "🔥", etc.
+    created_at: datetime = Field(default_factory=datetime.utcnow)
+    
+    user: User = Relationship()

backend/routers/social.py

@@ -3,8 +3,8 @@ from typing import List, Optional
 from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlmodel import Session, select, func
 from database import get_session
-from models import Comment, Rating, User, Profile
-from schemas import CommentCreate, CommentRead, RatingCreate, RatingRead
+from models import Comment, Rating, User, Profile, Reaction
+from schemas import CommentCreate, CommentRead, RatingCreate, RatingRead, ReactionCreate, ReactionRead
 from auth import get_current_user
 from helpers import create_notification
 
@@ -121,3 +121,71 @@ def get_average_rating(
         
     avg = session.exec(query).first()
     return float(avg) if avg else 0.0
+
+# --- Reactions ---
+
+@router.post("/reactions", response_model=ReactionRead)
+def toggle_reaction(
+    reaction: ReactionCreate,
+    session: Session = Depends(get_session),
+    current_user: User = Depends(get_current_user)
+):
+    query = select(Reaction).where(
+        Reaction.user_id == current_user.id,
+        Reaction.entity_type == reaction.entity_type,
+        Reaction.entity_id == reaction.entity_id
+    )
+    existing = session.exec(query).first()
+    
+    if existing:
+        if existing.emoji == reaction.emoji:
+            # Toggle off
+            session.delete(existing)
+            session.commit()
+            return existing 
+        else:
+            # Change emoji
+            existing.emoji = reaction.emoji
+            session.add(existing)
+            session.commit()
+            session.refresh(existing)
+            return existing
+    
+    # Create new
+    db_reaction = Reaction.model_validate(reaction)
+    db_reaction.user_id = current_user.id
+    session.add(db_reaction)
+    session.commit()
+    session.refresh(db_reaction)
+    
+    return db_reaction
+
+@router.get("/reactions/counts")
+def get_reaction_counts(
+    entity_type: str,
+    entity_id: int,
+    session: Session = Depends(get_session)
+):
+    # Group by emoji and count
+    query = select(Reaction.emoji, func.count(Reaction.id)).where(
+        Reaction.entity_type == entity_type,
+        Reaction.entity_id == entity_id
+    ).group_by(Reaction.emoji)
+    
+    results = session.exec(query).all()
+    # returns list of (emoji, count)
+    return {emoji: count for emoji, count in results}
+
+@router.get("/reactions/me")
+def get_my_reaction(
+    entity_type: str, 
+    entity_id: int, 
+    current_user: User = Depends(get_current_user),
+    session: Session = Depends(get_session)
+):
+    query = select(Reaction).where(
+        Reaction.user_id == current_user.id,
+        Reaction.entity_type == entity_type,
+        Reaction.entity_id == entity_id
+    )
+    return session.exec(query).first()

backend/schemas.py

@@ -346,3 +346,17 @@ class TagRead(TagBase):
 # Circular refs
 ShowRead.model_rebuild()
 PerformanceDetailRead.model_rebuild()
+
+# --- Reaction Schemas ---
+class ReactionBase(SQLModel):
+    entity_type: str
+    entity_id: int
+    emoji: str
+
+class ReactionCreate(ReactionBase):
+    pass
+
+class ReactionRead(ReactionBase):
+    id: int
+    user_id: int
+    created_at: datetime