feat: Add application-level settings for CSS color management

- Introduced a new table `application_setting` to store configurable application options.
- Implemented functions to manage CSS color settings, including loading, updating, and reading environment overrides.
- Added a new settings view to render and manage theme colors.
- Updated UI to include a settings page with theme color management and environment overrides display.
- Enhanced CSS styles for the settings page and sidebar navigation.
- Created unit and end-to-end tests for the new settings functionality and CSS management.

routes/ui.py

@@ -20,6 +20,12 @@ from routes.dependencies import get_db
 from services.reporting import generate_report
 from models.currency import Currency
 from routes.currencies import DEFAULT_CURRENCY_CODE, _ensure_default_currency
+from services.settings import (
+    CSS_COLOR_DEFAULTS,
+    get_css_color_settings,
+    list_css_env_override_rows,
+    read_css_color_env_overrides,
+)
 
 
 CURRENCY_CHOICES: list[Dict[str, Any]] = [
@@ -186,6 +192,20 @@ def _load_currency_settings(db: Session) -> Dict[str, Any]:
     }
 
 
+def _load_css_settings(db: Session) -> Dict[str, Any]:
+    variables = get_css_color_settings(db)
+    env_overrides = read_css_color_env_overrides()
+    env_rows = list_css_env_override_rows()
+    env_meta = {row["css_key"]: row for row in env_rows}
+    return {
+        "css_variables": variables,
+        "css_defaults": CSS_COLOR_DEFAULTS,
+        "css_env_overrides": env_overrides,
+        "css_env_override_rows": env_rows,
+        "css_env_override_meta": env_meta,
+    }
+
+
 def _load_consumption(db: Session) -> Dict[str, Any]:
     grouped: defaultdict[int, list[Dict[str, Any]]] = defaultdict(list)
     for record in (
@@ -672,6 +692,13 @@ async def reporting_view(request: Request, db: Session = Depends(get_db)):
     return _render(request, "reporting.html", _load_reporting(db))
 
 
+@router.get("/ui/settings", response_class=HTMLResponse)
+async def settings_view(request: Request, db: Session = Depends(get_db)):
+    """Render the settings landing page."""
+    context = _load_css_settings(db)
+    return _render(request, "settings.html", context)
+
+
 @router.get("/ui/currencies", response_class=HTMLResponse)
 async def currencies_view(request: Request, db: Session = Depends(get_db)):
     """Render the currency administration page with full currency context."""