Add Solarized dark mode to dashboard theme

[dbcli-symphony]

Changes

• Added Solarized Dark values under :root[data-theme="dark"], including #002b36, #073642, #93a1a1, and #859900.
• Updated status, chat, live status, and workflow chart styling to use Solarized-aware CSS variables in both light and dark modes.
• Added a regression test that verifies the dark-mode Solarized CSS tokens are present.

Tests

• pytest tests/test_web_app.py::test_dashboard_styles_define_solarized_dark_mode -vv
• ruff check .
• ruff format --check .
• mypy
• git diff --check