Add in-app account deletion (#319)

## Summary
- Add self-service deletion for the authenticated customer or subuser
identity only.
- Preserve shared customer grants, reset keys, bookings, order bookings,
vehicles, invoices, and legally required history.
- Require password/TOTP or a fresh deletion-specific, five-minute,
single-use WebAuthn assertion.
- Reject support impersonation and expired legacy plain-session tokens.
- Use durable database throttling, transactional request processing, a
durable outbox, and terminal `manual_review` state.
- Keep API and worker default-off behind separate
`account_deletion.api_enabled` and `account_deletion.worker_enabled`
module-config flags.

## Safe rollout
1. Keep both flags disabled.
2. Run `php scripts/account-deletion-schema.php check`.
3. If needed, run `php scripts/account-deletion-schema.php apply --yes`,
then rerun `check` until `ready:true`.
4. Deploy the frontend companion PR while the API remains disabled.
5. Enable `api_enabled` for a controlled canary; verify password and
passwordless request flows plus immediate authentication revocation.
6. Inspect queued request/outbox state, then enable `worker_enabled`.
7. Verify anonymization, preserved tenant/history data, outbox delivery,
retries, and manual-review behavior before broad rollout.

## Verification
- Account deletion unit tests: 2 passed, 43 assertions.
- PHP lint, both OpenAPI YAML parses, runtime-DDL scan,
destructive-scope scan, and `git diff --check` passed.
- Full API/unit/integration evidence is required from exact-head CI;
local Docker is unavailable and shared-vendor tests were explicitly
discarded.

## Security notes
- Schema mutation is CLI-only; web and cron paths perform read-only
readiness checks.
- Runtime behavior fails closed when schema/config/throttle/delivery
prerequisites are unavailable.

services/nginx/app/modules/account/cron/tasks.php

@@ -0,0 +1,16 @@
+<?php
+
+return [
+    [
+        'id' => 'account.process_deletion_requests',
+        'legacy_name' => 'ProcessAccountDeletionRequestsCron',
+        'name' => 'Process account deletion requests',
+        'description' => 'Anonymizes requested customer and chauffeur accounts while retaining legally required records.',
+        'module' => 'account',
+        'handler' => 'ProcessAccountDeletionRequestsCron',
+        'schedule' => ['type' => 'interval', 'seconds' => 300],
+        'timeout_seconds' => 300,
+        'estimated_duration_ms' => 2000,
+        'priority' => 25,
+    ],
+];