refactor(backend): clean up models setup, improve ip utils, add adr docs

- Extract ADR documents for architectural decisions (SQLite, FastAPI, React, APScheduler, Scheduler)
- Refactor setup.py: improve code structure and readability
- Add IP validation utilities with test coverage
- Update frontend components (BanTable, HistoryPage)
- Add pre-commit hooks and CONTRIBUTING.md
- Add .editorconfig for consistent coding standards

Docs/adr/ADR-003-React-Frontend-Framework.md

@@ -0,0 +1,37 @@
+# ADR-003: React over Vue
+
+## Status
+Accepted
+
+## Context
+The frontend requires a component-based SPA framework with strong typing, a
+battle-tested component library, and broad ecosystem support.
+
+## Decision
+Use **React 18+ with TypeScript** as the frontend framework.
+
+## Rationale
+
+### Why React over Vue?
+- **Ecosystem maturity:** React has the largest frontend ecosystem. Libraries
+  (date pickers, data grids, rich text editors) assume React availability first.
+- **Fluent UI v9:** Microsoft's official React component library is built for React.
+  The Vue-compatible version (Fluent UI Vue) lags significantly in features and
+  maintenance.
+- **Hiring and onboarding:** React is more widely known. New contributors are
+  more likely to arrive with React experience than Vue experience.
+- **Concurrent features:** React 18's concurrent rendering (`useTransition`,
+  `useDeferredValue`) provides a foundation for performance improvements in
+  data-heavy views like the ban table.
+
+### Why not Vue?
+- Fluent UI v9 does not provide first-class Vue support.
+- Vue's composition API is well-designed, but does not outweigh the Fluent UI
+  constraint.
+- Ecosystem and hiring advantages strongly favor React for enterprise-adjacent
+  projects.
+
+## Consequences
+- Frontend is a React SPA in `frontend/src/`.
+- All components are functional components using hooks.
+- Global state via React context (`frontend/src/providers/`).