fix(tests): read static sources as UTF-8 in the static assertion tests (#6850)

On native Windows the default text encoding is the ANSI code page
(cp1252 on en/pt systems), so the module-level read_text() calls in
eight static tests fail at collection with UnicodeDecodeError on bytes
0x81/0x90 that appear in static/js/chat.js, chatRenderer.js, app.js,
index.html and src/visual_report.py. Pass encoding="utf-8" like the
other 700+ tests in the suite already do.

Found by running the suite natively on Windows 11 (Python 3.11).

Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>
Co-authored-by: Alexandre Teixeira <general@alexandreteixeira.dev>

tests/test_agent_render_ownership.py

@@ -10,7 +10,7 @@ import unittest
 
 
 path = Path(__file__).resolve().parents[1] / "routes/chat_routes.py"
-tree = ast.parse(path.read_text())
+tree = ast.parse(path.read_text(encoding="utf-8"))
 node = next(n for n in tree.body if isinstance(n, ast.ClassDef) and n.name == "_AgentRenderState")
 namespace = {}
 exec(compile(ast.Module(body=[node], type_ignores=[]), str(path), "exec"), namespace)