refactor(migration): merge per-plugin SQL into single initial migration

Each plugin now has exactly one migration file (00001_initial.sql)
containing its complete table schema and seed data, replacing the
multi-file approach with split ALTER/INSERT steps.

Changes per plugin:
- auth: w_auth_sources, w_external_accounts, w_access_tokens + login session seed
- user: w_users + system user seed (removed w_access_tokens — belongs to auth)
- admin: w_system_configs, w_templates + all 32 config seeds + 2 template seeds
  (removed w_schedules, w_task_executions — belong to driver plugins)
- upload: w_upload_stats + indexes + access_mode + backfill
- message_gateway: all w_message_*, w_push_*, w_push_channels, w_push_histories
- risk_control/logstore: w_user_access_logs (PG + ClickHouse)
- driver_asynq_cron: w_schedules + cleanup seed
- driver_asynq_worker: w_task_executions

All CREATE TABLE use IF NOT EXISTS, all INSERT use ON CONFLICT DO NOTHING.
go:embed patterns remain 'migrations/*.sql' — unchanged.

plugins/domain/user/migrations/00001_initial.sql

@@ -0,0 +1,36 @@
+-- +goose Up
+-- +goose StatementBegin
+CREATE TABLE IF NOT EXISTS w_users (
+    id BIGINT PRIMARY KEY,
+    username VARCHAR(64) NOT NULL UNIQUE,
+    password VARCHAR(255),
+    nickname VARCHAR(255),
+    email VARCHAR(255),
+    avatar_url VARCHAR(255),
+    is_active BOOLEAN DEFAULT TRUE,
+    is_admin BOOLEAN DEFAULT FALSE,
+    bio VARCHAR(500),
+    phone VARCHAR(32),
+    gender VARCHAR(16),
+    website VARCHAR(255),
+    location VARCHAR(255),
+    last_login_at TIMESTAMPTZ,
+    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP
+);
+CREATE INDEX IF NOT EXISTS idx_w_users_email ON w_users (email);
+CREATE INDEX IF NOT EXISTS idx_w_users_is_active ON w_users (is_active);
+CREATE INDEX IF NOT EXISTS idx_w_users_last_login_at ON w_users (last_login_at);
+CREATE INDEX IF NOT EXISTS idx_w_users_created_at ON w_users (created_at);
+
+-- Seed system user
+INSERT INTO w_users (id, username, password, nickname, avatar_url, is_active, is_admin, last_login_at, created_at, updated_at)
+VALUES (999, 'system', '*', '系统', '', TRUE, FALSE, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+ON CONFLICT (username) DO NOTHING;
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+DELETE FROM w_users WHERE username = 'system';
+DROP TABLE IF EXISTS w_users;
+-- +goose StatementEnd