feat: Add 15 backend service stub files with TODO implementations

Stub files for all services declared in services/mod.rs:
- Panel adapters: AMP, Pterodactyl, Companion (NATS-based)
- Wipe pipeline: WipeEngine, Scheduler, HealthChecker, BackupManager
- Infrastructure: NatsBridge (JetStream), SteamUpdateWatcher, MapManager
- Notifications: Discord webhooks, Pushbullet push notifications
- Platform: LicenseService, CloudflareService, encryption utilities

Each file has struct definitions, method signatures with proper types,
and descriptive TODO comments outlining the implementation plan.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/services/scheduler.rs

@@ -0,0 +1,56 @@
+use anyhow::Result;
+use chrono::{DateTime, Utc};
+use uuid::Uuid;
+
+/// Cron-based wipe schedule management.
+///
+/// Manages wipe schedules backed by `tokio-cron-scheduler`. Each schedule
+/// maps a cron expression + timezone to a wipe profile. When a schedule
+/// fires, it creates a wipe_history record and dispatches execution to
+/// the WipeEngine.
+pub struct SchedulerService {
+    // TODO: Add fields:
+    // - db: sqlx::PgPool
+    // - nats: async_nats::Client
+    // - scheduler: tokio_cron_scheduler::JobScheduler
+}
+
+impl SchedulerService {
+    /// Start the scheduler, loading all active schedules from the database.
+    pub async fn start(&self) -> Result<()> {
+        // TODO: Query all active wipe_schedules from DB
+        // TODO: Register each as a cron job in tokio-cron-scheduler
+        // TODO: Start the scheduler event loop
+        todo!()
+    }
+
+    /// Register a wipe schedule as a cron job.
+    pub async fn register_wipe_schedule(&self, _schedule_id: Uuid) -> Result<()> {
+        // TODO: Load WipeSchedule from DB
+        // TODO: Parse cron_expression with timezone
+        // TODO: Create tokio-cron-scheduler job that:
+        //   1. Creates a wipe_history record
+        //   2. Publishes wipe execution event to NATS
+        // TODO: Store job handle for later removal
+        todo!()
+    }
+
+    /// Remove a schedule from the running scheduler.
+    pub async fn remove_schedule(&self, _schedule_id: Uuid) -> Result<()> {
+        // TODO: Look up job handle by schedule_id
+        // TODO: Remove from tokio-cron-scheduler
+        todo!()
+    }
+
+    /// Calculate the next N scheduled run times for a given schedule.
+    pub async fn get_next_runs(
+        &self,
+        _schedule_id: Uuid,
+        _count: usize,
+    ) -> Result<Vec<DateTime<Utc>>> {
+        // TODO: Load cron_expression and timezone from DB
+        // TODO: Iterate cron expression to compute next N fire times
+        // TODO: Convert to UTC and return
+        todo!()
+    }
+}