Add Dockerfile and script for containerized Playwright testing

- Add `Dockerfile` based on `mcr.microsoft.com/playwright:v1.57.0-jammy`.
- Add `scripts/run-playwright-docker.sh` to build and run the container with volume mounts.
- Add `.dockerignore` to prevent host `node_modules` from corrupting the build.
- Update `README.md` with usage instructions.

scripts/run-playwright-docker.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+set -e
+
+# Build the Docker image
+echo "Building Docker image bitvid-playwright..."
+docker build -t bitvid-playwright .
+
+# Check if arguments are provided, default to "npm run test:visual" if not
+if [ $# -eq 0 ]; then
+    CMD="npm run test:visual"
+else
+    CMD="$@"
+fi
+
+echo "Running: $CMD"
+
+# Run the container
+# - --rm: Remove container after exit
+# - -it: Interactive terminal
+# - --ipc=host: Recommended for Playwright to avoid memory issues
+# - -v $(pwd):/app: Mount current directory to /app for live code updates and artifacts
+# - -v /app/node_modules: Anonymous volume to preserve container's node_modules (prevents host node_modules from overriding)
+# - -w /app: Set working directory
+docker run --rm -it --ipc=host \
+    -v "$(pwd):/app" \
+    -v /app/node_modules \
+    -w /app \
+    bitvid-playwright \
+    $CMD