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.

models/application_setting.py

@@ -0,0 +1,29 @@
+from datetime import datetime
+from typing import Optional
+
+from sqlalchemy import Boolean, DateTime, String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+from sqlalchemy.sql import func
+
+from config.database import Base
+
+
+class ApplicationSetting(Base):
+    __tablename__ = "application_setting"
+
+    id: Mapped[int] = mapped_column(primary_key=True, index=True)
+    key: Mapped[str] = mapped_column(String(128), unique=True, nullable=False)
+    value: Mapped[str] = mapped_column(Text, nullable=False)
+    value_type: Mapped[str] = mapped_column(String(32), nullable=False, default="string")
+    category: Mapped[str] = mapped_column(String(32), nullable=False, default="general")
+    description: Mapped[Optional[str]] = mapped_column(Text, nullable=True)
+    is_editable: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), nullable=False
+    )
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now(), nullable=False
+    )
+
+    def __repr__(self) -> str:
+        return f"<ApplicationSetting key={self.key} category={self.category}>"