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

@@ -0,0 +1,19 @@
+# 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.