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/settings.py

@@ -0,0 +1,85 @@
+from typing import Dict, List
+
+from fastapi import APIRouter, Depends, HTTPException, status
+from pydantic import BaseModel, Field, model_validator
+from sqlalchemy.orm import Session
+
+from routes.dependencies import get_db
+from services.settings import (
+    CSS_COLOR_DEFAULTS,
+    get_css_color_settings,
+    list_css_env_override_rows,
+    read_css_color_env_overrides,
+    update_css_color_settings,
+)
+
+router = APIRouter(prefix="/api/settings", tags=["Settings"])
+
+
+class CSSSettingsPayload(BaseModel):
+    variables: Dict[str, str] = Field(default_factory=dict)
+
+    @model_validator(mode="after")
+    def _validate_allowed_keys(self) -> "CSSSettingsPayload":
+        invalid = set(self.variables.keys()) - set(CSS_COLOR_DEFAULTS.keys())
+        if invalid:
+            invalid_keys = ", ".join(sorted(invalid))
+            raise ValueError(
+                f"Unsupported CSS variables: {invalid_keys}."
+                " Accepted keys align with the default theme variables."
+            )
+        return self
+
+
+class EnvOverride(BaseModel):
+    css_key: str
+    env_var: str
+    value: str
+
+
+class CSSSettingsResponse(BaseModel):
+    variables: Dict[str, str]
+    env_overrides: Dict[str, str] = Field(default_factory=dict)
+    env_sources: List[EnvOverride] = Field(default_factory=list)
+
+
+@router.get("/css", response_model=CSSSettingsResponse)
+def read_css_settings(db: Session = Depends(get_db)) -> CSSSettingsResponse:
+    try:
+        values = get_css_color_settings(db)
+        env_overrides = read_css_color_env_overrides()
+        env_sources = [
+            EnvOverride(**row)
+            for row in list_css_env_override_rows()
+        ]
+    except ValueError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail=str(exc),
+        ) from exc
+    return CSSSettingsResponse(
+        variables=values,
+        env_overrides=env_overrides,
+        env_sources=env_sources,
+    )
+
+
+@router.put("/css", response_model=CSSSettingsResponse, status_code=status.HTTP_200_OK)
+def update_css_settings(payload: CSSSettingsPayload, db: Session = Depends(get_db)) -> CSSSettingsResponse:
+    try:
+        values = update_css_color_settings(db, payload.variables)
+        env_overrides = read_css_color_env_overrides()
+        env_sources = [
+            EnvOverride(**row)
+            for row in list_css_env_override_rows()
+        ]
+    except ValueError as exc:
+        raise HTTPException(
+            status_code=status.HTTP_422_UNPROCESSABLE_ENTITY,
+            detail=str(exc),
+        ) from exc
+    return CSSSettingsResponse(
+        variables=values,
+        env_overrides=env_overrides,
+        env_sources=env_sources,
+    )

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."""