Add genlocke creation wizard with backend API and 4-step frontend

Implements the genlocke creation feature end-to-end: Genlocke and
GenlockeLeg models with migration, POST /genlockes endpoint that
creates the genlocke with all legs and auto-starts the first run,
and a 4-step wizard UI (Name, Select Games with preset templates,
Rules, Confirm) at /genlockes/new.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/api/genlockes.py

@@ -0,0 +1,81 @@
+from fastapi import APIRouter, Depends, HTTPException
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import selectinload
+
+from app.core.database import get_session
+from app.models.game import Game
+from app.models.genlocke import Genlocke, GenlockeLeg
+from app.models.nuzlocke_run import NuzlockeRun
+from app.schemas.genlocke import GenlockeCreate, GenlockeResponse
+
+router = APIRouter()
+
+
+@router.post("", response_model=GenlockeResponse, status_code=201)
+async def create_genlocke(
+    data: GenlockeCreate, session: AsyncSession = Depends(get_session)
+):
+    if not data.game_ids:
+        raise HTTPException(status_code=400, detail="At least one game is required")
+
+    if not data.name.strip():
+        raise HTTPException(status_code=400, detail="Name is required")
+
+    # Validate all game_ids exist
+    result = await session.execute(
+        select(Game).where(Game.id.in_(data.game_ids))
+    )
+    found_games = {g.id: g for g in result.scalars().all()}
+    missing = [gid for gid in data.game_ids if gid not in found_games]
+    if missing:
+        raise HTTPException(
+            status_code=404, detail=f"Games not found: {missing}"
+        )
+
+    # Create genlocke
+    genlocke = Genlocke(
+        name=data.name.strip(),
+        status="active",
+        genlocke_rules=data.genlocke_rules,
+        nuzlocke_rules=data.nuzlocke_rules,
+    )
+    session.add(genlocke)
+    await session.flush()  # get genlocke.id
+
+    # Create legs
+    legs = []
+    for i, game_id in enumerate(data.game_ids, start=1):
+        leg = GenlockeLeg(
+            genlocke_id=genlocke.id,
+            game_id=game_id,
+            leg_order=i,
+        )
+        session.add(leg)
+        legs.append(leg)
+
+    # Create the first run
+    first_game = found_games[data.game_ids[0]]
+    first_run = NuzlockeRun(
+        game_id=first_game.id,
+        name=f"{data.name.strip()} \u2014 Leg 1",
+        status="active",
+        rules=data.nuzlocke_rules,
+    )
+    session.add(first_run)
+    await session.flush()  # get first_run.id
+
+    # Link first leg to the run
+    legs[0].run_id = first_run.id
+
+    await session.commit()
+
+    # Reload with relationships
+    result = await session.execute(
+        select(Genlocke)
+        .where(Genlocke.id == genlocke.id)
+        .options(
+            selectinload(Genlocke.legs).selectinload(GenlockeLeg.game),
+        )
+    )
+    return result.scalar_one()