docs: Document all environment variables

docs/environment.md

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+# Environment Variables
+
+This page lists all the environment variables that can be used to configure the container.
+
+## 🪟 Windows
+
+| Variable | Default | Description |
+|---|---|---|
+| `VERSION` | `11` | Windows version to install, for example `10` or `11`. |
+| `EDITION` |  | Windows edition to install, for example `core` for Windows Server Core. |
+| `LANGUAGE` | `en-US` | Windows display language, for example `en`, `fr`, `nl`, etc. |
+| `REGION` | `en-US` | Windows regional format, for example `en-US`. |
+| `KEYBOARD` | `en-US` | Keyboard layout used during installation, for example `en-US`. |
+| `USERNAME` | `Dockur` | Username for the Windows account. |
+| `PASSWORD` | `admin` | Password for the Windows account. |
+| `KEY` |  | Windows product key used during installation. |
+| `MANUAL` | `N` | Enables manual installation instead of unattended installation. |
+| `VERIFY` | `N` | Verifies checksums of downloaded images. |
+| `REMOVE` | `Y` | Removes the Windows ISO after installation. Set to `N` to keep it. |
+
+## 🧠 CPU and Memory
+
+| Variable | Default | Description |
+|---|---|---|
+| `CPU_CORES` | `2` | Number of CPU cores assigned to the VM. Can also be set to `max` or `half`. |
+| `CPU_MODEL` | `host` | QEMU CPU model to use. |
+| `CPU_FLAGS` |  | Additional QEMU CPU flags. |
+| `KVM` | `Y` | Enables KVM hardware acceleration. Set to `N` to disable. |
+| `VMX` | `N` | Exposes Intel VMX virtualization extensions to Windows. |
+| `HV` | `Y` | Enables Hyper-V enlightenments for Windows. |
+| `RAM_SIZE` | `4G` | Amount of RAM assigned to the VM, for example `4G`, `8G`, `max`, or `half`. |
+| `RAM_CHECK` | `Y` | Checks whether enough host memory is available before starting the VM. |
+
+## ⚙️ System
+
+| Variable | Default | Description |
+|---|---|---|
+| `MACHINE` | `q35` | QEMU machine type. |
+| `UUID` |  | QEMU VM UUID. |
+| `HPET` | `off` | Enables or disables the QEMU HPET timer. |
+| `VMPORT` | `off` | Enables or disables the QEMU VMware port. |
+| `SM_BIOS` |  | Additional SMBIOS arguments passed to QEMU. |
+| `ARGUMENTS` |  | Additional raw QEMU arguments appended to the generated command line. |
+
+## 🚀 Boot
+
+| Variable | Default | Description |
+|---|---|---|
+| `BOOT_MODE` | `windows` | Boot mode, for example `windows`, `windows_secure`, or `windows_legacy`. |
+| `BOOT_INDEX` | `9` | Boot priority index for the installation media. |
+| `BIOS` |  | Custom BIOS/firmware file. Setting this enables custom boot mode. |
+| `TPM` | `N` | Enables TPM support. |
+| `SMM` | `N` | Enables SMM/secure-machine support. |
+| `LOGO` | `Y` | Enables the custom boot logo. |
+| `CLEAR` | `N` | Clears the firmware/NVRAM variables on the next boot. |
+| `USB` | `qemu-xhci,id=xhci,p2=7,p3=7` | QEMU USB controller setting. Set to a `no*` value to disable. |
+
+## 💾 Storage
+
+| Variable | Default | Description |
+|---|---|---|
+| `DISK_SIZE` | `64G` | Size of the main data disk. |
+| `DISK_FMT` | `raw` | Disk image format, usually `raw` or `qcow2`. |
+| `DISK_TYPE` | `scsi` | Disk controller/device type, such as `sata`, `scsi`, `nvme`, or `blk`. |
+| `DISK_CACHE` | `none` | QEMU disk cache mode, for example `none` or `writeback`. |
+| `DISK_IO` | `native` | QEMU disk I/O mode, for example `native`, `threads`, or `io_uring`. |
+| `DISK_DISCARD` | `unmap` | Enables TRIM/unmap support for the data disk. |
+| `DISK_ROTATION` | `1` | Rotation rate reported to the guest. Use `1` for SSD-like storage. |
+| `DISK_FLAGS` |  | Additional options used when creating qcow2 disks. |
+| `ALLOCATE` | `N` | Preallocates disk space when creating the data disk. |
+| `STORAGE` | `/storage` | Storage directory used for disks, firmware variables, and generated files. |
+
+## 🌐 Networking
+
+| Variable | Default | Description |
+|---|---|---|
+| `NETWORK` | `Y` | Network mode. Common values are `Y` for NAT, `passt`, `slirp`, or `N` to disable networking. |
+| `DHCP` | `N` | Enables DHCP/macvtap mode so the VM receives an address from the external LAN. |
+| `IP` |  | Guest IP address override. |
+| `MAC` |  | Guest network adapter MAC address. |
+| `HOST` | `Windows` | Hostname assigned to the VM. |
+| `DEV` | `eth0` | Host/container network interface to use. |
+| `MTU` |  | Network MTU to use for the guest interface. |
+| `MASK` | `255.255.255.0` | IPv4 netmask. |
+| `TAP` | `qemu` | TAP/macvtap interface name. |
+| `BRIDGE` | `docker` | Bridge name used for NAT networking. |
+| `ADAPTER` | `virtio-net-pci` | QEMU network adapter model. |
+| `HOST_PORTS` |  | Ports reserved for services running on the host/container side. |
+| `USER_PORTS` |  | Additional ports to forward to the VM when using user-mode networking. |
+| `DNSMASQ_OPTS` |  | Additional dnsmasq options. |
+| `DNSMASQ_DEBUG` | `N` | Enables dnsmasq log tailing. |
+| `DNSMASQ_DISABLE` | `N` | Disables the internal dnsmasq resolver. |
+| `PASST_OPTS` |  | Additional passt options. |
+| `PASST_DEBUG` | `N` | Enables passt debug output. |
+
+## 📁 File Sharing
+
+| Variable | Default | Description |
+|---|---|---|
+| `SAMBA` | `Y` | Enables or disables the Samba shared folder. |
+| `SAMBA_DEBUG` | `N` | Enables Samba debug output. |
+
+## 🖥️ Display
+
+| Variable | Default | Description |
+|---|---|---|
+| `WIDTH` | `1920` | Display width configured for Windows. |
+| `HEIGHT` | `1080` | Display height configured for Windows. |
+| `DISPLAY` | `web` | Display backend. Common values are `web`, `vnc`, `disabled`, or `none`. |
+| `VGA` | `virtio` | QEMU video adapter model. |
+| `GPU` | `N` | Enables Intel iGPU acceleration. Experimental. |
+| `RENDERNODE` | `/dev/dri/renderD128` | Render node used for GPU acceleration. |
+
+## 🌍 Web UI
+
+| Variable | Default | Description |
+|---|---|---|
+| `WEB` | `Y` | Enables or disables the web interface. |
+| `WEB_PORT` | `8006` | Port for the web interface. |
+| `VNC_PORT` | `5900` | Port for the VNC server. |
+| `WSS_PORT` | `5700` | WebSocket port used by QEMU/noVNC. |
+| `WSD_PORT` | `8004` | Internal websocketd port. |
+| `PROTECT` | `N` | Enables password protection for the web interface. |
+
+## 🎈 Memory Ballooning
+
+| Variable | Default | Description |
+|---|---|---|
+| `BALLOONING` | `N` | Enables dynamic memory ballooning. |
+| `BALLOONING_DEBUG` | `N` | Enables debug output for the ballooning monitor. |
+| `BALLOONING_MIN_MEM` | `33%` | Minimum memory target for the balloon device. |
+| `BALLOONING_RAM_THRESHOLD` | `80.0` | Target host RAM usage percentage. |
+| `BALLOONING_RAM_THRESHOLD_HARD` | `90.0` | Host RAM usage percentage where ballooning becomes more aggressive. |
+| `BALLOONING_PSI_PRESSURE` | `10.0` | PSI memory pressure level where ballooning starts reacting more aggressively. |
+| `BALLOONING_PSI_PRESSURE_MAX` | `50.0` | PSI memory pressure level where ballooning reaches its strongest response. |
+| `BALLOONING_HYSTERESIS` | `128M` | Minimum memory change before the balloon target is updated. |
+| `BALLOONING_KP` | `0.5` | Proportional gain for the ballooning controller. |
+| `BALLOONING_KI` | `0.05` | Integral gain for the ballooning controller. |
+| `BALLOONING_INTERVAL` | `5` | Polling interval in seconds. |
+
+## 🔌 Shutdown
+
+| Variable | Default | Description |
+|---|---|---|
+| `SHUTDOWN` | `Y` | Enables graceful ACPI shutdown. |
+| `TIMEOUT` | `115` | Timeout used while waiting for the VM to shut down. |
+
+## 🐞 Debugging
+
+| Variable | Default | Description |
+|---|---|---|
+| `DEBUG` | `N` | Enables verbose debug output. |
+| `TRACE` | `N` | Enables shell command tracing. |
+| `DETECTED` |  | Overrides the detected Windows image identifier. |
+| `SERIAL` | `mon:stdio` | QEMU serial device setting. |
+| `MONITOR` | `unix:$QEMU_DIR/monitor.sock,server,wait=off,nodelay` | QEMU monitor device setting. |