feat: migrate frontend from Vue 3 to React 18 with TanStack ecosystem

- Complete rewrite of frontend using React 18 + TypeScript in strict mode
- Implement TanStack Router for file-based routing matching URL structure
- Use TanStack Query for server state management with smart caching
- Replace Pinia stores with React Context API for auth and UI state
- Adopt Tailwind CSS + shadcn/ui components for consistent styling
- Switch from pnpm to Bun for faster package management and builds
- Configure Vite to support React, TypeScript, and modern tooling
- Create frontend.go with Go embed package for embedding dist/ in binary
- Implement comprehensive TypeScript interfaces (strict mode, no 'any' types)
- Add dark mode support throughout with Tailwind CSS dark: classes
- Set up i18n infrastructure (English translations included)
- Remove all Vue 3 code, components, stores, CSS, and assets
- Includes 18 new files with ~2000 lines of production-ready code

frontend/frontend.go

@@ -0,0 +1,14 @@
+package frontend
+
+import (
+	"embed"
+)
+
+//go:embed dist
+var dist embed.FS
+
+// Assets returns the embedded frontend filesystem.
+// The dist directory is embedded and will be accessed as "dist/..." by fs.Sub
+func Assets() embed.FS {
+	return dist
+}