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/drivers/driver_asynq_cron/migrations/00001_initial.sql

@@ -0,0 +1,20 @@
+-- +goose Up
+CREATE TABLE IF NOT EXISTS w_schedules (
+    id BIGINT PRIMARY KEY,
+    name VARCHAR(128) NOT NULL,
+    task_type VARCHAR(64) NOT NULL,
+    cron VARCHAR(64) NOT NULL,
+    payload TEXT,
+    is_active BOOLEAN NOT NULL DEFAULT TRUE,
+    created_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP,
+    updated_at TIMESTAMPTZ DEFAULT CURRENT_TIMESTAMP
+);
+CREATE INDEX IF NOT EXISTS idx_w_schedules_is_active ON w_schedules (is_active);
+
+-- Seed initial cleanup task
+INSERT INTO w_schedules (id, name, task_type, cron, payload, is_active, created_at, updated_at)
+VALUES (1, '系统定期垃圾清理', 'system_cleanup', '0 3 * * *', '{}', TRUE, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+ON CONFLICT (id) DO NOTHING;
+
+-- +goose Down
+DROP TABLE IF EXISTS w_schedules;