WP-02: encrypted settings, SMTP mail, job runner and cron scheduler

AES-256-GCM secret storage keyed by MASTER_KEY, SMTP settings with test mail
(lettre), persisted job runs with log and status, JobRunner with per-kind
concurrency guard, 6-field cron schedules with defaults, scheduler loop.
Settings and Jobs pages in the UI. FAKE_HOST mode for dev machines.

Tests: 30 application, 8 infrastructure, 23 API, 16 Vitest, 6 Playwright.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backend/crates/api/src/openapi.rs

@@ -24,6 +24,8 @@ impl Modify for BearerAuth {
     paths(
         crate::auth::login, crate::auth::refresh, crate::auth::logout, crate::auth::me,
         crate::users::list, crate::users::create, crate::users::get_one, crate::users::update, crate::users::reset_password,
+        crate::settings::get_smtp, crate::settings::put_smtp, crate::settings::test_smtp, crate::settings::list_schedules, crate::settings::put_schedule,
+        crate::jobs::list, crate::jobs::kinds, crate::jobs::get_one, crate::jobs::run,
     ),
     modifiers(&BearerAuth)
 )]