fix(electron-backend): avoid double-gunzipping EPG responses

Stop treating content-encoding as a manual gunzip signal, because fetch already returns decoded bodies for transfer-compressed XMLTV responses.

Keep redirect and payload-based gzip detection in place, and add regression coverage for redirected .gz feeds, gzip MIME types, content-disposition filenames, and plain content-encoding responses.

Entire-Checkpoint: c6e522b4276c

apps/electron-backend/src/app/workers/epg-response-utils.spec.ts

@@ -19,12 +19,32 @@ describe('shouldGunzipEpgResponse', () => {
         ).toBe(true);
     });
 
-    it('returns true for gzip content-encoding even without a .gz path', () => {
+    it('returns false for gzip content-encoding without a gzip payload', () => {
         expect(
             shouldGunzipEpgResponse('https://example.com/guide', {
                 headers: new Headers([['content-encoding', 'gzip']]),
                 url: 'https://example.com/guide',
             })
+        ).toBe(false);
+    });
+
+    it('returns true for gzip mime types', () => {
+        expect(
+            shouldGunzipEpgResponse('https://example.com/guide', {
+                headers: new Headers([['content-type', 'application/gzip']]),
+                url: 'https://example.com/guide',
+            })
+        ).toBe(true);
+    });
+
+    it('returns true when content-disposition advertises a .gz filename', () => {
+        expect(
+            shouldGunzipEpgResponse('https://example.com/guide', {
+                headers: new Headers([
+                    ['content-disposition', 'attachment; filename="guide.xml.gz"'],
+                ]),
+                url: 'https://example.com/guide',
+            })
         ).toBe(true);
     });
 

apps/electron-backend/src/app/workers/epg-response-utils.ts

@@ -22,11 +22,6 @@ export function shouldGunzipEpgResponse(
         return true;
     }
 
-    const contentEncoding = response.headers.get('content-encoding');
-    if (contentEncoding?.toLowerCase().includes('gzip')) {
-        return true;
-    }
-
     const contentType = response.headers.get('content-type');
     if (
         contentType &&