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/amp_adapter.rs

@@ -0,0 +1,86 @@
+use anyhow::Result;
+use async_trait::async_trait;
+
+use super::panel_adapter::{DiscoveredServer, FileEntry, PanelAdapter, ServerStatus};
+
+/// AMP (Application Management Panel) adapter.
+///
+/// Communicates with AMP instances via their REST API to manage
+/// Rust game servers. Implements the unified PanelAdapter trait
+/// so the wipe engine and other services remain panel-agnostic.
+pub struct AmpAdapter {
+    pub api_endpoint: String,
+    pub api_key: String,
+}
+
+impl AmpAdapter {
+    pub fn new(api_endpoint: String, api_key: String) -> Self {
+        Self {
+            api_endpoint,
+            api_key,
+        }
+    }
+}
+
+#[async_trait]
+impl PanelAdapter for AmpAdapter {
+    async fn test_connection(&self) -> Result<bool> {
+        // TODO: POST to AMP API /API/Core/Login, verify session token returned
+        todo!()
+    }
+
+    async fn discover_servers(&self) -> Result<Vec<DiscoveredServer>> {
+        // TODO: GET instances from AMP API, map to DiscoveredServer
+        todo!()
+    }
+
+    async fn get_server_status(&self, _server_id: &str) -> Result<ServerStatus> {
+        // TODO: Query AMP instance status endpoint
+        todo!()
+    }
+
+    async fn start_server(&self, _server_id: &str) -> Result<()> {
+        // TODO: POST to AMP API /API/Core/Start
+        todo!()
+    }
+
+    async fn stop_server(&self, _server_id: &str) -> Result<()> {
+        // TODO: POST to AMP API /API/Core/Stop
+        todo!()
+    }
+
+    async fn restart_server(&self, _server_id: &str) -> Result<()> {
+        // TODO: POST to AMP API /API/Core/Restart
+        todo!()
+    }
+
+    async fn send_command(&self, _server_id: &str, _command: &str) -> Result<String> {
+        // TODO: POST to AMP API /API/Core/SendConsoleMessage
+        todo!()
+    }
+
+    async fn get_file(&self, _server_id: &str, _path: &str) -> Result<Vec<u8>> {
+        // TODO: GET file contents via AMP file manager API
+        todo!()
+    }
+
+    async fn put_file(&self, _server_id: &str, _path: &str, _data: &[u8]) -> Result<()> {
+        // TODO: Upload file via AMP file manager API
+        todo!()
+    }
+
+    async fn delete_file(&self, _server_id: &str, _path: &str) -> Result<()> {
+        // TODO: DELETE file via AMP file manager API
+        todo!()
+    }
+
+    async fn list_files(&self, _server_id: &str, _path: &str) -> Result<Vec<FileEntry>> {
+        // TODO: GET directory listing from AMP file manager API
+        todo!()
+    }
+
+    async fn trigger_steam_update(&self, _server_id: &str) -> Result<()> {
+        // TODO: POST to AMP API /API/Core/Update to trigger SteamCMD
+        todo!()
+    }
+}