Phase 5 red: collection and file decryption tests

10 tests covering decryptCollection (key + name decryption from raw
server JSON, type mapping, isShared, missing name, wrong key) and
decryptFile (key + metadata decryption, fileType number-to-string
mapping, file/thumbnail header passthrough, wrong key).

Adds src/model/types.ts with both raw (server) and decrypted (library)
type definitions. src/model/decrypt.ts has throwing stubs.

src/model/index.ts

@@ -0,0 +1,12 @@
+export { decryptCollection, decryptFile } from "./decrypt.js";
+export type {
+    Collection,
+    CollectionType,
+    EnteFile,
+    FileBlob,
+    FileMetadata,
+    FileType,
+    Microseconds,
+    RawCollection,
+    RawEnteFile,
+} from "./types.js";