docs(docker): enhance GPU installation instructions and update script behavior

surfsense_web/content/docs/docker-installation/docker-compose.mdx

@@ -55,10 +55,50 @@ SurfSense publishes CPU and CUDA backend image variants. The frontend image is n
 
 All backend variants are published for `linux/amd64` and `linux/arm64`. CUDA on `linux/arm64` is best-effort.
 
-<Callout type="warn">
-`SURFSENSE_VARIANT` only selects the GPU-built backend image. GPU device access is added separately in Phase 3.
+<Callout type="info">
+GPU acceleration needs two settings: `SURFSENSE_VARIANT` selects the CUDA image, and `COMPOSE_FILE` enables the GPU device overlay. The host must have the NVIDIA Container Toolkit installed.
 </Callout>
 
+### NVIDIA GPU Acceleration
+
+For most NVIDIA systems, add these values to `.env` to use the CUDA 12.8 image:
+
+```dotenv
+SURFSENSE_VARIANT=cuda
+COMPOSE_FILE=docker-compose.yml:docker-compose.gpu.yml
+SURFSENSE_GPU_COUNT=1
+```
+
+Use `SURFSENSE_VARIANT=cuda126` for older NVIDIA driver stacks or older GPUs that need the CUDA 12.6 fallback image.
+
+On Windows, use `;` instead of `:` in `COMPOSE_FILE` inside `.env`:
+
+```dotenv
+COMPOSE_FILE=docker-compose.yml;docker-compose.gpu.yml
+```
+
+To switch variants later, edit `SURFSENSE_VARIANT` and `COMPOSE_FILE` in `.env`, then run:
+
+```bash
+docker compose pull
+docker compose up -d --wait
+```
+
+### Automatic Updates
+
+Manual Docker Compose installs do not start Watchtower automatically. To enable external automatic updates, run Watchtower separately:
+
+```bash
+docker run -d --name watchtower \
+  --restart unless-stopped \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  nickfedor/watchtower \
+  --label-enable \
+  --interval 86400
+```
+
+SurfSense containers are labeled for Watchtower, so `--label-enable` limits updates to the SurfSense services.
+
 ### Ports
 
 | Variable | Description | Default |

surfsense_web/content/docs/docker-installation/install-script.mdx

@@ -3,7 +3,7 @@ title: One-Line Install Script
 description: One-command installation of SurfSense using Docker
 ---
 
-Downloads the compose files, generates a `SECRET_KEY`, starts all services, and sets up [Watchtower](https://github.com/nicholas-fedor/watchtower) for automatic daily updates.
+Downloads the compose files, generates a `SECRET_KEY`, starts all services with `docker compose up -d --wait`, and starts [Watchtower](https://github.com/nicholas-fedor/watchtower) as an external updater for automatic daily updates.
 
 **Prerequisites:** [Docker Desktop](https://www.docker.com/products/docker-desktop/) must be installed and running.
 
@@ -19,7 +19,34 @@ curl -fsSL https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scr
 irm https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scripts/install.ps1 | iex
 ```
 
-This creates a `./surfsense/` directory with `docker-compose.yml` and `.env`, then runs `docker compose up -d`.
+This creates a `./surfsense/` directory with `docker-compose.yml`, `docker-compose.gpu.yml`, and `.env`, then runs `docker compose up -d --wait`.
+
+If an NVIDIA GPU and NVIDIA Container Toolkit are detected, the installer prompts for the backend variant. Non-interactive installs default to CPU unless you pass an explicit flag.
+
+### GPU options
+
+Linux/macOS:
+
+```bash
+# CUDA 12.8
+curl -fsSL https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scripts/install.sh | bash -s -- --variant=cuda
+
+# CUDA 12.6 fallback for older driver stacks
+curl -fsSL https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scripts/install.sh | bash -s -- --variant=cuda126
+
+# Reserve all available GPUs
+curl -fsSL https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scripts/install.sh | bash -s -- --gpu --gpu-count=all
+```
+
+PowerShell:
+
+```powershell
+# Save the script locally first when passing PowerShell parameters.
+.\install.ps1 -Variant cuda
+.\install.ps1 -Variant cuda126 -GpuCount all
+```
+
+The installer writes the same `.env` settings you would configure manually: `SURFSENSE_VARIANT` selects the backend image and `COMPOSE_FILE` enables the GPU overlay.
 
 To skip Watchtower (e.g. in production where you manage updates yourself):
 
@@ -29,6 +56,16 @@ curl -fsSL https://raw.githubusercontent.com/MODSetter/SurfSense/main/docker/scr
 
 To customise the check interval (default 24h), use `--watchtower-interval=SECONDS`.
 
+Manual updates use the same compose state stored in `.env`, so GPU overlays and variants are preserved:
+
+```bash
+cd surfsense
+docker compose pull
+docker compose up -d --wait
+```
+
+If Watchtower is enabled, it preserves the running image variant tag automatically. Because SurfSense images are large, use `--no-watchtower` when you prefer to manage update timing yourself.
+
 ---
 
 ## Access SurfSense