docs: add Windows quickstart + Docker Desktop notes

docs/windows-quickstart.md

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+# Windows Quickstart — Lappa
+
+> Step-by-step guide to install and run **Lappa** on Windows 10 / 11.
+
+---
+
+## Prerequisites
+
+| Requirement | Notes |
+| --- | --- |
+| **Windows 10** (22H2+) or **Windows 11** | x86-64 only; ARM via x64 emulation is experimental |
+| **Python 3.11+** | Download from [python.org](https://www.python.org/downloads/) — check **"Add to PATH"** during install |
+| **Git** (optional) | [git-scm.com](https://git-scm.com/) or use `winget install Git.Git` |
+| **Docker Desktop** (optional) | Required only for real ROS2 container mode — see [Docker notes](#docker-desktop-notes) |
+
+---
+
+## Install from source
+
+### 1. Clone or download
+
+```powershell
+git clone https://github.com/mergeos-bounties/Lappa.git
+cd Lappa
+```
+
+> No Git? Download the [latest ZIP](https://github.com/mergeos-bounties/Lappa/archive/refs/heads/main.zip) and extract.
+
+### 2. Create a virtual environment
+
+```powershell
+cd packages\server
+python -m venv .venv
+.\.venv\Scripts\activate
+```
+
+### 3. Install Lappa
+
+```powershell
+pip install -e ".[dev,api,gui]"
+```
+
+### 4. Verify
+
+```powershell
+lappa version
+```
+
+You should see version output (e.g. `0.4.0`).
+
+---
+
+## Run
+
+### Browser IDE (recommended)
+
+```powershell
+lappa serve --port 8840
+```
+
+Open **http://127.0.0.1:8840** in your browser. Load a demo from the explorer and press **▶ Run Sim**.
+
+### Desktop GUI (native Qt)
+
+```powershell
+lappa-gui
+```
+
+### Offline smoke test
+
+```powershell
+lappa demo
+```
+
+---
+
+## Docker Desktop notes
+
+Docker is **optional** — the native kinematics sim works entirely offline without it. Use Docker only when you need real `ros2 launch` commands and full ROS2 distribution fidelity.
+
+### Setup
+
+1. Install [Docker Desktop for Windows](https://www.docker.com/products/docker-desktop/)
+2. Launch Docker Desktop — **WSL 2 backend** is recommended
+3. Verify:
+
+   ```powershell
+   docker --version
+   docker compose version
+   ```
+
+### Start the ROS2 runtime
+
+```powershell
+# From repository root
+docker compose -f packages/docker/docker-compose.yml up --build
+```
+
+Or use **Lappa IDE → Docker → Start runtime**.
+
+### Notes
+
+- Docker Desktop requires a restart after first install.
+- Containers use the **host network** mode — the IDE at `localhost:8840` communicates directly.
+- If you see **"Docker Desktop requires a newer WSL kernel"**, run `wsl --update` from an admin PowerShell.
+- On resource-constrained machines, increase Docker Desktop memory to at least **4 GB** (Settings → Resources → Advanced).
+
+---
+
+## Troubleshooting
+
+| Symptom | Fix |
+| --- | --- |
+| `python` not found | Re-run Python installer — check **"Add to PATH"** |
+| `pip` fails with long-path error | Open PowerShell as Admin: `New-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Control\FileSystem" -Name "LongPathsEnabled" -Value 1 -PropertyType DWORD -Force` |
+| `lappa` command not found | Ensure `.venv\Scripts` is active — run `.\.venv\Scripts\activate` |
+| Docker compose not found | Docker Desktop may still be starting; wait and retry |
+| Port 8840 in use | `lappa serve --port 8841` |
+
+---
+
+## See also
+
+- [README](../README.md) — full project overview
+- [CLI reference](../README.md#cli-reference)
+- [Docker setup](../README.md#docker-optional)
+- [Roadmap](ROADMAP.md)