fix(http): drop APIHelper's hand-set brotli encoding; LogoHelper sends the real UA

APIHelper advertised `br` though brotli isn't installed, so a server that
honoured it would send a body requests can't decode. LogoHelper sent a bare
`LEDMatrix-Common/1.0`, the kind of User-Agent ESPN has been rejecting.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/test_http_headers.py

@@ -33,6 +33,13 @@ class TestSharedHeaders:
     def test_api_helper_sends_the_same_user_agent(self):
         assert APIHelper().session.headers['User-Agent'] == USER_AGENT
 
+    def test_api_helper_does_not_hand_set_brotli(self):
+        assert 'br' not in APIHelper().session.headers.get('Accept-Encoding', '')
+
+    def test_logo_helper_sends_the_same_user_agent(self):
+        from src.common.logo_helper import LogoHelper
+        assert LogoHelper(display_width=64, display_height=32).session.headers['User-Agent'] == USER_AGENT
+
 
 class TestLogoDownloaderHeaders:
     def test_uses_the_shared_headers(self):

test/test_logo_helper.py

@@ -424,7 +424,8 @@ class TestPlaceholderLogo:
 
 class TestSessionConfiguration:
     def test_user_agent_and_accept_headers(self, helper):
-        assert helper.session.headers["User-Agent"] == "LEDMatrix-Common/1.0"
+        from src.common.api_helper import USER_AGENT
+        assert helper.session.headers["User-Agent"] == USER_AGENT
         assert helper.session.headers["Accept"] == "image/*"