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/infrastructure/Cargo.toml

@@ -7,10 +7,13 @@ license.workspace = true
 [dependencies]
 domain.workspace = true
 anyhow.workspace = true
+aes-gcm = "0.10"
 argon2.workspace = true
+base64.workspace = true
 async-trait.workspace = true
 chrono.workspace = true
 jsonwebtoken.workspace = true
+lettre = { version = "0.11", default-features = false, features = ["builder", "smtp-transport", "tokio1", "tokio1-rustls-tls", "hostname"] }
 serde.workspace = true
 sqlx.workspace = true
 uuid.workspace = true