Add genlocke leg progression with advance endpoint and run context

When a run belonging to a genlocke is completed or failed, the genlocke
status updates accordingly. The run detail API now includes genlocke
context (leg order, total legs, genlocke name). A new advance endpoint
creates the next leg's run, and the frontend shows genlocke-aware UI
including a "Leg X of Y" banner, advance button, and contextual
messaging in the end-run modal.

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

backend/src/app/api/genlockes.py

@@ -79,3 +79,86 @@ async def create_genlocke(
         )
     )
     return result.scalar_one()
+
+
+@router.post(
+    "/{genlocke_id}/legs/{leg_order}/advance",
+    response_model=GenlockeResponse,
+)
+async def advance_leg(
+    genlocke_id: int,
+    leg_order: int,
+    session: AsyncSession = Depends(get_session),
+):
+    # Load genlocke with legs
+    result = await session.execute(
+        select(Genlocke)
+        .where(Genlocke.id == genlocke_id)
+        .options(
+            selectinload(Genlocke.legs).selectinload(GenlockeLeg.game),
+        )
+    )
+    genlocke = result.scalar_one_or_none()
+    if genlocke is None:
+        raise HTTPException(status_code=404, detail="Genlocke not found")
+
+    if genlocke.status != "active":
+        raise HTTPException(
+            status_code=400, detail="Genlocke is not active"
+        )
+
+    # Find the current leg
+    current_leg = None
+    next_leg = None
+    for leg in genlocke.legs:
+        if leg.leg_order == leg_order:
+            current_leg = leg
+        elif leg.leg_order == leg_order + 1:
+            next_leg = leg
+
+    if current_leg is None:
+        raise HTTPException(status_code=404, detail="Leg not found")
+
+    # Verify current leg's run is completed
+    if current_leg.run_id is None:
+        raise HTTPException(
+            status_code=400, detail="Current leg has no run"
+        )
+    current_run = await session.get(NuzlockeRun, current_leg.run_id)
+    if current_run is None or current_run.status != "completed":
+        raise HTTPException(
+            status_code=400, detail="Current leg's run is not completed"
+        )
+
+    if next_leg is None:
+        raise HTTPException(
+            status_code=400, detail="No next leg to advance to"
+        )
+
+    if next_leg.run_id is not None:
+        raise HTTPException(
+            status_code=400, detail="Next leg already has a run"
+        )
+
+    # Create a new run for the next leg
+    new_run = NuzlockeRun(
+        game_id=next_leg.game_id,
+        name=f"{genlocke.name} \u2014 Leg {next_leg.leg_order}",
+        status="active",
+        rules=genlocke.nuzlocke_rules,
+    )
+    session.add(new_run)
+    await session.flush()
+
+    next_leg.run_id = new_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()