feat: 添加数据库迁移脚本和 Supabase 工具配置

添加迁移脚本以支持数据库版本管理，配置 pnpm workspace 仅构建 supabase 依赖
新增用户登录字段和任务帮助请求功能，禁用 tasks 和 task_steps 表的 RLS
更新环境变量示例以支持自托管 Supabase 实例

supabase/migrations/20260128000002_add_help_request_fields.sql

@@ -0,0 +1,56 @@
+alter table public.tasks
+  add column if not exists help_requested_to_user_id uuid null,
+  add column if not exists help_requested_by_user_id uuid null,
+  add column if not exists help_requested_at timestamptz null;
+
+alter table public.task_steps
+  add column if not exists help_requested_to_user_id uuid null,
+  add column if not exists help_requested_by_user_id uuid null,
+  add column if not exists help_requested_at timestamptz null;
+
+do $$
+begin
+  if not exists (
+    select 1 from pg_constraint where conname = 'tasks_help_requested_to_user_id_fkey'
+  ) then
+    alter table public.tasks
+      add constraint tasks_help_requested_to_user_id_fkey
+      foreign key (help_requested_to_user_id) references public.users(id);
+  end if;
+
+  if not exists (
+    select 1 from pg_constraint where conname = 'tasks_help_requested_by_user_id_fkey'
+  ) then
+    alter table public.tasks
+      add constraint tasks_help_requested_by_user_id_fkey
+      foreign key (help_requested_by_user_id) references public.users(id);
+  end if;
+
+  if not exists (
+    select 1 from pg_constraint where conname = 'task_steps_help_requested_to_user_id_fkey'
+  ) then
+    alter table public.task_steps
+      add constraint task_steps_help_requested_to_user_id_fkey
+      foreign key (help_requested_to_user_id) references public.users(id);
+  end if;
+
+  if not exists (
+    select 1 from pg_constraint where conname = 'task_steps_help_requested_by_user_id_fkey'
+  ) then
+    alter table public.task_steps
+      add constraint task_steps_help_requested_by_user_id_fkey
+      foreign key (help_requested_by_user_id) references public.users(id);
+  end if;
+end $$;
+
+create index if not exists tasks_help_requested_to_user_id_idx
+  on public.tasks(help_requested_to_user_id);
+
+create index if not exists tasks_help_requested_by_user_id_idx
+  on public.tasks(help_requested_by_user_id);
+
+create index if not exists task_steps_help_requested_to_user_id_idx
+  on public.task_steps(help_requested_to_user_id);
+
+create index if not exists task_steps_help_requested_by_user_id_idx
+  on public.task_steps(help_requested_by_user_id);