fix: use request-first TemplateResponse signature

Modern Starlette requires `request` as the first positional arg to
TemplateResponse. The old `TemplateResponse(name, context)` form caused
the context dict to be passed as the template name, which Jinja2 then
tried to use as a cache key -> TypeError: unhashable type: 'dict' (500
on GET / and /roster).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/main.py

@@ -76,12 +76,12 @@ app.include_router(routers.router)
 
 @app.get("/", response_class=HTMLResponse)
 def index(request: Request):
-    return templates.TemplateResponse("index.html", {"request": request})
+    return templates.TemplateResponse(request, "index.html")
 
 
 @app.get("/roster", response_class=HTMLResponse)
 def roster(request: Request):
-    return templates.TemplateResponse("roster.html", {"request": request})
+    return templates.TemplateResponse(request, "roster.html")
 
 
 @app.get("/health")