Fix: Restore Native caching business logic and implement 3-mode launcher

- Implemented Default, Onsite, and Native launcher modes in launcher_file_cont.svelte.
- Restored background pre-caching logic with configurable timers in new LauncherBackgroundSync component.
- Fixed standard browser download regression for regular website mode.
- Modernized electron_relay to TypeScript and standardized bridge detection in layout.
- Detailed startup and background sync technical flow in documentation.

src/lib/electron/electron_relay.ts

@@ -0,0 +1,123 @@
+/**
+ * Aether Electron Relay (V3)
+ * Maps legacy launcher commands to the modern Aether Native Bridge.
+ */
+
+const log_lvl = 1;
+
+/**
+ * Returns the native bridge if available.
+ */
+function getBridge() {
+    if (typeof window !== 'undefined' && (window as any).aetherNative) {
+        return (window as any).aetherNative;
+    }
+    return null;
+}
+
+/**
+ * Open a local directory in the OS File Manager.
+ */
+export async function open_folder(path: string) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+    
+    if (log_lvl) console.log(`Relay: Opening folder: ${path}`);
+    return await bridge.openFolder(path);
+}
+
+/**
+ * Launch a file using the OS default application.
+ */
+export async function launch_file(path: string) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+    
+    if (log_lvl) console.log(`Relay: Launching file: ${path}`);
+    return await bridge.launchFile(path);
+}
+
+/**
+ * Legacy compatibility alias for launch_file.
+ */
+export const open_local_file_v2 = async ({ file_path, filename }: { file_path: string, filename: string }) => {
+    return launch_file(`${file_path}/${filename}`);
+};
+
+/**
+ * Run a shell command.
+ */
+export async function run_cmd({ cmd, return_stdout = true }: { cmd: string, return_stdout?: boolean }) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+    
+    if (log_lvl) console.log(`Relay: Running command: ${cmd}`);
+    const result = await bridge.runCommand(cmd);
+    
+    if (return_stdout) return result.stdout;
+    return result.success;
+}
+
+/**
+ * Legacy compatibility alias for run_cmd.
+ */
+export const run_cmd_sync = run_cmd;
+
+/**
+ * Kill specific processes by name.
+ */
+export async function kill_processes({ process_name_li = [] }: { process_name_li: string[] }) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+
+    for (const name of process_name_li) {
+        if (log_lvl) console.log(`Relay: Killing process: ${name}`);
+        await bridge.runCommand(`pkill -f "${name}"`);
+    }
+    return true;
+}
+
+/**
+ * Check if a file hash exists in the local cache.
+ */
+export async function check_hash_file_cache({ cacheRoot, hash }: { cacheRoot: string, hash: string }) {
+    const bridge = getBridge();
+    if (!bridge) return false;
+    return await bridge.checkCache({ cacheRoot, hash });
+}
+
+/**
+ * Download a file to the local cache.
+ */
+export async function download_to_cache({ url, cacheRoot, hash, apiKey }: { url: string, cacheRoot: string, hash: string, apiKey: string }) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+    return await bridge.downloadToCache({ url, cacheRoot, hash, apiKey });
+}
+
+/**
+ * Launch a file from the local cache (copies to temp first).
+ */
+export async function launch_from_cache({ cacheRoot, hash, tempRoot, filename }: { cacheRoot: string, hash: string, tempRoot: string, filename: string }) {
+    const bridge = getBridge();
+    if (!bridge) return { success: false, error: 'Native bridge not found' };
+    return await bridge.launchFromCache({ cacheRoot, hash, tempRoot, filename });
+}
+
+/**
+ * Get system/device info.
+ */
+export async function get_device_info() {
+    const bridge = getBridge();
+    if (!bridge) return null;
+    return await bridge.getDeviceConfig();
+}
+
+/**
+ * Placeholder for legacy AppleScript execution.
+ */
+export async function run_osascript({ cmd }: { cmd: string }) {
+    const bridge = getBridge();
+    if (!bridge) return null;
+    return await bridge.runCommand(`osascript -e '${cmd}'`);
+}