v2.26.0: fix SSE fanout crash and branded logo FOUC

- Fix SSE fanout thread AttributeError when source queue is None during
  interpreter shutdown by snapshotting to local variable with null guard
- Fix branded "i" logo rendering oversized on first page load (FOUC) by
  adding inline width/height to SVG elements across 10 templates
- Bump version to 2.26.0 in config.py, pyproject.toml, and CHANGELOG.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/test_routes.py

@@ -1,8 +1,9 @@
 """Tests for Flask routes and API endpoints."""
 
 import json
+from unittest.mock import MagicMock, patch
+
 import pytest
-from unittest.mock import patch, MagicMock
 
 
 @pytest.fixture(scope='session')