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_controller.py

@@ -11,9 +11,10 @@ Tests cover:
 
 import json
 import os
-import pytest
 import sys
-from unittest.mock import Mock, patch, MagicMock
+from unittest.mock import Mock, patch
+
+import pytest
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
@@ -51,6 +52,7 @@ def setup_db(tmp_path):
 def app(setup_db):
     """Create Flask app with controller blueprint."""
     from flask import Flask
+
     from routes.controller import controller_bp
 
     app = Flask(__name__)