fix(app): preserve file line endings and UTF-8 BOM (#2277)

* fix(app): preserve file line endings and UTF-8 BOM

* refactor(app): simplify line ending preservation

Let the editor parse newline variants and serialize with the file's first separator. Mixed-ending files become uniform on edit without a separate normalization layer.

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Co-authored-by: Mohamed Boudra <boudra.moha@gmail.com>

packages/app/src/stores/session-store.ts

@@ -278,6 +278,8 @@ export interface ExplorerFile {
   kind: ExplorerFileKind;
   encoding: ExplorerEncoding;
   content?: string;
+  // TextDecoder removes a leading UTF-8 BOM; retain this bit so file writes can restore it.
+  hasBom: boolean;
   mimeType?: string;
   size: number;
   modifiedAt: string;