Fix Tailwind asset build dropping all utility classes in Docker

The Dockerfile asset stage copied only static/src + vite.config.js, never
the HTML templates. Tailwind v4 generates CSS by scanning source files for
class usage, so with no templates present it emitted a stripped CSS with
zero utility classes — breaking layout and ballooning SVG icons (w-5/h-5
no longer applied) on deployed builds.

- main.css: add explicit @source directive for the templates dir so content
  detection no longer depends on the build CWD.
- Dockerfile: copy vergabe_teilnahme/templates into the assets stage so the
  @source path resolves at build time.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Dockerfile

@@ -16,6 +16,10 @@ COPY package.json package-lock.json ./
 RUN npm ci --no-audit --no-fund
 COPY vite.config.js ./
 COPY static/src ./static/src
+# Tailwind v4 scans these for utility-class usage at build time. They must be
+# present or the generated CSS omits every utility class (broken layout, giant
+# SVG icons). Paths mirror the @source directive in static/src/main.css.
+COPY vergabe_teilnahme/templates ./vergabe_teilnahme/templates
 RUN npm run build
 # Output: /build/static/dist/main.css