feat(e2e): add Docker-based E2E test isolation

Add Docker setup for running E2E tests with the Angular dev server
containerized while Playwright runs on the host. Supports multiple
instances via configurable ports.

New files:
- Dockerfile.e2e.dev: Dev server image
- docker-compose.e2e.yaml: E2E orchestration config
- scripts/wait-for-app.sh: Health check script

New npm scripts:
- e2e:docker: Run E2E with containerized app
- e2e:docker:webdav: Same but includes WebDAV for sync tests

Usage: APP_PORT=4343 npm run e2e:docker

Dockerfile.e2e.dev

@@ -0,0 +1,20 @@
+FROM node:22-bookworm
+
+# Install Angular CLI globally and curl for healthcheck
+RUN npm install -g @angular/cli && apt-get update && apt-get install -y curl && rm -rf /var/lib/apt/lists/*
+
+WORKDIR /app
+
+# Copy everything (source needed for prepare script during npm install)
+COPY . .
+
+# Install dependencies
+RUN npm install --legacy-peer-deps
+
+# Default port (can be overridden via environment variable)
+ENV APP_PORT=4242
+
+EXPOSE ${APP_PORT}
+
+# Start Angular dev server with dynamic port
+CMD ["sh", "-c", "ng serve --port ${APP_PORT} --host 0.0.0.0"]