fix(docker): copy tailwind+postcss config so CSS compiles in build

Build produced 308-byte stub CSS (raw @tailwind directives, unprocessed)
instead of real 27KB compiled stylesheet. Dockerfile missed copying
tailwind.config.js + postcss.config.js into build context. Page rendered
as unstyled white text.

Added COPY for both configs. Rebuild: CSS now 27146 bytes. App styled.

docker/Dockerfile

@@ -13,6 +13,7 @@ COPY shared/ ./shared/
 COPY server/ ./server/
 COPY src/ ./src/
 COPY public/ ./public/
+COPY tailwind.config.js postcss.config.js ./
 
 # better-sqlite3 native build (alpine musl)
 RUN cd server && npm rebuild better-sqlite3