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

@@ -13,7 +13,7 @@ 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, '清理未使用上传', 'cleanup_unused_uploads', '0 */2 * * *', '{}', TRUE, CURRENT_TIMESTAMP, CURRENT_TIMESTAMP)
+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

plugins/drivers/driver_asynq_cron/migrations/00002_alter_schedules_identity.sql

@@ -1,5 +0,0 @@
--- +goose Up
-ALTER TABLE w_schedules ALTER COLUMN id ADD GENERATED BY DEFAULT AS IDENTITY (START WITH 100);
-
--- +goose Down
-ALTER TABLE w_schedules ALTER COLUMN id DROP IDENTITY IF EXISTS;

plugins/drivers/driver_asynq_cron/migrations/00003_update_cleanup_schedule.sql

@@ -1,11 +0,0 @@
--- +goose Up
-UPDATE w_schedules
-SET name = '系统定期垃圾清理',
-    task_type = 'system_cleanup'
-WHERE id = 1;
-
--- +goose Down
-UPDATE w_schedules
-SET name = '清理未使用上传',
-    task_type = 'cleanup_unused_uploads'
-WHERE id = 1;