docs: reorganize documentation into server/ and web/ directories

- docs: move server docs to docs/server/ and update all cross-references
- docs: move web-roadmap.md to docs/web/roadmap.md and create
  docs/web/decisions.md
- docs: update AGENTS.md with separate Server and Web sections

docs/web/decisions.md

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+# Technical Decisions
+
+## 2026-07-14: Client-rendered Web Foundation
+
+**Context**: MyGO needs a browser client now and native clients later. The Web application must share the versioned REST API instead of introducing browser-only server logic.
+
+**Decisions**:
+
+| Area | Choice | Guidance |
+|------|--------|----------|
+| Rendering | Pure client-side rendered SPA | Vite emits static assets; do not introduce SSR, React Server Components, or a Node API server. |
+| Application stack | React, strict TypeScript, React Router, and TanStack Query | Keep routing and remote-data state explicit and client-side. |
+| UI system | Ant Design plus Tailwind CSS 4 | Ant Design owns reusable controls and theme tokens; Tailwind initially owns layout, spacing, and responsive utilities. |
+| Dependency policy | Install capabilities when their feature starts | Keep API generation, transfer, virtualization, drag-and-drop, test, and preview libraries deferred in `docs/web/roadmap.md`. |
+
+**Consequences**:
+- The Web and future native clients consume the same client-neutral API contracts.
+- MyGO or a reverse proxy may host `web/dist` with an SPA fallback without changing the rendering model.
+- MyGO domain components own file-browser behavior and must not depend on Ant Design request behavior for business logic.

docs/web/roadmap.md

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+# Web Roadmap
+
+## Product Boundary
+
+- The Web client is a pure client-side rendered single-page application.
+- Vite produces static assets only. The project does not use SSR, React Server Components, a Node API server, or a browser-specific business backend.
+- The Web client consumes the same versioned REST API as future Android and other native clients.
+- Production may serve `web/dist` from MyGO or a reverse proxy.
+- Shared API contracts should remain client-neutral and eventually be described by OpenAPI.
+
+## Foundation
+
+The initial project contains only the framework and styling foundation:
+
+- Node.js 24 and npm
+- Vite
+- React
+- TypeScript in strict mode
+- TanStack Query provider
+- Tailwind CSS 4 through its Vite plugin
+- Ant Design provider and components
+- Oxlint from the Vite template
+
+Ant Design owns reusable UI components and theme tokens. Tailwind CSS is initially limited to application layout, spacing, and responsive utilities.
+
+## Planned Structure
+
+```text
+web/src/
+├── app/          # Router, providers, and application composition
+├── api/          # API client and generated contracts
+├── components/   # Shared presentation components
+├── features/     # Auth, files, account, and admin features
+├── pages/        # Route entry points
+├── lib/          # Framework-independent utilities
+└── test/         # Shared test setup and fixtures
+```
+
+## Deferred Dependencies
+
+Some dependencies are suggested for future implementation. Refer these only when the corresponding feature is implemented and propose better choices if any:
+
+- `@ant-design/icons`: Add Ant Design-consistent application and action icons when real screens require them.
+- `openapi-typescript`: Generate TypeScript API types from the shared OpenAPI document.
+- `openapi-fetch`: Provide a small type-safe Fetch client based on generated OpenAPI types.
+- `openapi-react-query`: Connect generated OpenAPI operations to TanStack Query if handwritten query adapters become repetitive.
+- `zustand`: Manage a cross-route upload queue, bulk selection, or other complex client-only state if React state is insufficient.
+- `vitest`: Run unit and integration tests using the Vite toolchain.
+- `pdfjs-dist`: Preview PDF files in the browser when document preview is implemented.