fix admin template collision with auth/dashboard blueprints

Namespace admin templates under admin/ subdirectory to prevent
Quart's template loader from resolving auth's login.html and
dashboard's index.html instead of admin's own templates.

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

padelnomics/src/padelnomics/admin/routes.py

@@ -189,7 +189,7 @@ async def login():
         else:
             await flash("Invalid password.", "error")
     
-    return await render_template("login.html")
+    return await render_template("admin/login.html")
 
 
 @bp.route("/logout", methods=["POST"])
@@ -210,7 +210,7 @@ async def index():
     failed_tasks = await get_failed_tasks()
     
     return await render_template(
-        "index.html",
+        "admin/index.html",
         stats=stats,
         recent_users=recent_users,
         failed_tasks=failed_tasks,
@@ -229,7 +229,7 @@ async def users():
     user_list = await get_users(limit=per_page, offset=offset, search=search or None)
     
     return await render_template(
-        "users.html",
+        "admin/users.html",
         users=user_list,
         search=search,
         page=page,
@@ -245,7 +245,7 @@ async def user_detail(user_id: int):
         await flash("User not found.", "error")
         return redirect(url_for("admin.users"))
     
-    return await render_template("user_detail.html", user=user)
+    return await render_template("admin/user_detail.html", user=user)
 
 
 @bp.route("/users/<int:user_id>/impersonate", methods=["POST"])
@@ -284,7 +284,7 @@ async def tasks():
     failed = await get_failed_tasks()
     
     return await render_template(
-        "tasks.html",
+        "admin/tasks.html",
         tasks=task_list,
         failed_tasks=failed,
     )