docs: update architecture and development docs to cover client workspace

- add client workspace section to architecture diagram and description
- split development.md commands into server and client per-workspace
- document client tech stack, directory layout, routing, and theming
- add Client overview section with Storybook test instructions

docs/architecture.md

@@ -1,11 +1,19 @@
 # Architecture
 
 ```
+┌─────────────────────────────────────────┐
+│  Browser  (React SPA — client/)         │
+│                                         │
+│  EnvironmentsPage  KeysPage             │
+│  SessionsPage      ScenariosPage        │
+└───────────────────┬─────────────────────┘
+                    │ HTTP REST  (:13000)
+                    │
 MCP client (AI agent / VS Code Copilot)
         │  HTTP /mcp  (Streamable MCP)
         ▼
 ┌──────────────────────────────────────┐
-│  NestJS app  (src/)                  │
+│  NestJS app  (server/src/)           │
 │                                      │
 │  McpService         ← all MCP tools  │
 │                                      │
@@ -32,3 +40,11 @@ MCP client (AI agent / VS Code Copilot)
 - **CodeExecutorService** — compiles and runs user-supplied Playwright JS inside a sandboxed `async` function with `page`, `context`, and `helpers` in scope.
 - **ScenarioService** — CRUD for scenarios, steps, runs, and run logs; import/export.
 - **ScenarioSchedulerService** — polls for pending step runs every second and executes them. All steps in the same run share **one browser instance** (see [scenario.md](scenario.md)).
+
+## Client (`client/`)
+
+A React 19 + TypeScript SPA served separately by Vite during development. In Docker Compose the same build artefacts are served statically alongside the API.
+
+The client calls the server REST endpoints directly — there is no separate BFF layer. Routing uses HashRouter so the Vite proxy and server-side routes are never ambiguous.
+
+See [development.md](development.md) for the full client tech stack and directory layout.