feat: hard-delete instead of soft-delete; rename app/account secret tables

[BK1031]

• Drop DeletedAt from Account, Application, AppSecret, Secret
• Switch every soft-delete (Updates({deleted_at: now})) to actual gorm.Delete
• Strip every AND deleted_at IS NULL filter (no longer meaningful)
• Cascade Account → child Secret rows in a transaction (mirrors the existing Application → AppSecret cascade)
• Drop entityID args from DeleteAccount(WithAudit) / DeleteApplication / DeleteAppSecret / DeleteSecret (the audit-log struct already carries actor info)
• Switch the partial unique indexes (idx_application_name_live, idx_app_secret_application_key_live — only enforced where deleted_at IS NULL) to plain uniqueIndex — this is what unblocks re-creating something with the same name
• Rename vault_secret → vault_account_secret, vault_app_secret → vault_application_secret. vault_account + vault_application already match the convention

Pre-deploy SQL migration

Run against gr-postgres.gauchoracing.com / db vault BEFORE rolling out the new image, otherwise AutoMigrate will create empty vault_account_secret / vault_application_secret tables and leave the live data orphaned in the old names.

BEGIN;

-- 1. Drop any rows we had previously soft-deleted (they would otherwise reappear as live rows).
DELETE FROM vault_app_secret    WHERE deleted_at IS NOT NULL;
DELETE FROM vault_application   WHERE deleted_at IS NOT NULL;
DELETE FROM vault_secret        WHERE deleted_at IS NOT NULL;
DELETE FROM vault_account       WHERE deleted_at IS NOT NULL;

-- 2. Drop the partial unique indexes — AutoMigrate will replace with full uniqueIndex.
DROP INDEX IF EXISTS idx_application_name_live;
DROP INDEX IF EXISTS idx_app_secret_application_key_live;

-- 3. Rename the secret tables.
ALTER TABLE vault_secret     RENAME TO vault_account_secret;
ALTER TABLE vault_app_secret RENAME TO vault_application_secret;

-- 4. Drop the now-dead deleted_at columns (AutoMigrate would otherwise leave them as unused dead columns).
ALTER TABLE vault_account            DROP COLUMN IF EXISTS deleted_at;
ALTER TABLE vault_account_secret     DROP COLUMN IF EXISTS deleted_at;
ALTER TABLE vault_application        DROP COLUMN IF EXISTS deleted_at;
ALTER TABLE vault_application_secret DROP COLUMN IF EXISTS deleted_at;

COMMIT;

After this, AutoMigrate on the next deploy adds the new uniqueIndex on vault_application(name) and vault_application_secret(application_id, key).