Sanitize file names taken from server metadata (closes #9)

A file title or album name decrypted from server data could name a path
outside the chosen directory (`../../.ssh/authorized_keys`). One module,
src/filename.ts, now makes such names safe for `quak get`/`get-thumb`
without `--out`, downloadFile/downloadThumbnail without outPath, and the
backup and metadata backup trees. Originals-cache extensions are limited to
letters and digits. A user-supplied path is still used as is. decryptFile
reads a missing or non-string title as "" and rejects metadata that is not
a JSON object.

Model: opus-5-5

src/download/index.ts

@@ -11,6 +11,7 @@ import {
     streamTagFinal,
 } from "../crypto/index.js";
 import { TruncatedStreamError } from "../errors.js";
+import { sanitizeFileName } from "../filename.js";
 import { withRetry } from "../retry.js";
 import type { ApiClient } from "../api/client.js";
 import type { EnteFile } from "../model/types.js";
@@ -286,7 +287,10 @@ export const downloadFile = async (
     outPath?: string,
     onProgress?: ProgressCallback,
 ): Promise<DownloadResult> => {
-    const resolvedPath = outPath ?? file.metadata.title;
+    // `outPath` is the caller's and is used as is; the title is the server's
+    // and is sanitized so it can only name a file in the current directory.
+    const resolvedPath =
+        outPath ?? sanitizeFileName(file.metadata.title, `file-${file.id}`);
     const header = fromBase64(file.file.decryptionHeader);
     const bytesWritten = await fetchAndDecrypt(
         api,
@@ -305,7 +309,9 @@ export const downloadThumbnail = async (
     outPath?: string,
     onProgress?: ProgressCallback,
 ): Promise<DownloadResult> => {
-    const resolvedPath = outPath ?? `thumb_${file.metadata.title}`;
+    const resolvedPath =
+        outPath ??
+        `thumb_${sanitizeFileName(file.metadata.title, `file-${file.id}`)}`;
     const header = fromBase64(file.thumbnail.decryptionHeader);
     const bytesWritten = await fetchAndDecrypt(
         api,