feat: add initial implementation of ECS architecture and systems

- Introduced a minimal Entity-Component-System (ECS) framework in `ecs.ts` with basic entity management and component handling.
- Created `World` class to manage entities and components, including methods for creating, adding, retrieving, and removing components.
- Implemented unit tests for the `World` class in `ecs.test.ts` to ensure functionality.
- Developed input handling with `InputSystem` to capture keyboard events.
- Added `PhysicsSystem` for movement and collision detection.
- Created `RenderSystem` to handle drawing entities on the canvas.
- Set up a main game loop in `main.ts` to integrate systems and manage game state.
- Added SVG icons and images for UI elements.
- Included CSS styles for layout and theming.
- Configured TypeScript settings in `tsconfig.json` for project compilation.

Co-authored-by: Copilot <copilot@github.com>

README.md

@@ -0,0 +1,41 @@
+# ZAMNY Client
+
+Vite + TypeScript + Canvas 2D + ECS game client for _Zombies Ate My Neighbors_ browser edition.
+
+## Quick Start
+
+```bash
+npm install
+npm run dev          # http://localhost:5173
+npm test             # vitest (ECS tests)
+npm run build
+```
+
+## Structure
+
+```txt
+src/
+  engine/
+    ecs.ts           # World, Entity, Component, System base
+    ecs.test.ts      # 6 unit tests (green)
+  systems/
+    InputSystem.ts   # keyboard/touch stub
+    RenderSystem.ts  # Canvas 2D stub
+    PhysicsSystem.ts # movement/collision stub
+  main.ts            # 60 FPS game loop + system orchestration
+```
+
+## Key Points
+
+- ECS core: `createEntity`, `addComponent`, `query`, `destroyEntity`
+- Systems extend `System` and implement `update(world, dt)`
+- Target: 60 FPS, offline single-player works without server
+- Nickname UI, NetworkClient, sprite rendering: TODO
+
+## Testing
+
+- Vitest + jsdom
+- `npm test` runs `ecs.test.ts`
+- Coverage target: 70% (documented in ARCHITECTURE.md §10)
+
+See root [README.md](../README.md) and [ARCHITECTURE.md](../ARCHITECTURE.md) for full design.