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/upload/migrations/00001_initial.sql

@@ -0,0 +1,49 @@
+-- +goose Up
+-- +goose StatementBegin
+CREATE TABLE IF NOT EXISTS w_upload_stats (
+    dimension VARCHAR(32) NOT NULL,
+    stat_key VARCHAR(64) NOT NULL DEFAULT '',
+    file_count BIGINT NOT NULL DEFAULT 0,
+    file_size BIGINT NOT NULL DEFAULT 0,
+    updated_at TIMESTAMPTZ NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    PRIMARY KEY (dimension, stat_key)
+);
+
+CREATE INDEX IF NOT EXISTS idx_w_uploads_status_created_at ON w_uploads (status, created_at);
+CREATE INDEX IF NOT EXISTS idx_w_uploads_hash_file_size_status ON w_uploads (hash, file_size, status);
+
+ALTER TABLE w_uploads ADD COLUMN IF NOT EXISTS access_mode INTEGER NOT NULL DEFAULT 0;
+UPDATE w_uploads SET access_mode = 1 WHERE type = 'avatar';
+
+-- Backfill upload stats
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT 'total', '', COUNT(*), COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+
+INSERT INTO w_upload_stats (dimension, stat_key, file_count, file_size)
+SELECT
+    'type',
+    COALESCE(NULLIF(type, ''), 'generic'),
+    COUNT(*),
+    COALESCE(SUM(file_size), 0)
+FROM w_uploads
+WHERE status != 'deleted'
+GROUP BY COALESCE(NULLIF(type, ''), 'generic')
+ON CONFLICT (dimension, stat_key) DO UPDATE SET
+    file_count = EXCLUDED.file_count,
+    file_size = EXCLUDED.file_size,
+    updated_at = CURRENT_TIMESTAMP;
+-- +goose StatementEnd
+
+-- +goose Down
+-- +goose StatementBegin
+DROP TABLE IF EXISTS w_upload_stats;
+DROP INDEX IF EXISTS idx_w_uploads_hash_file_size_status;
+DROP INDEX IF EXISTS idx_w_uploads_status_created_at;
+ALTER TABLE w_uploads DROP COLUMN IF EXISTS access_mode;
+-- +goose StatementEnd