fix(web): add missing postcss.config.mjs + copy into Docker build

Without postcss.config.mjs, @tailwindcss/postcss never ran during
'next build', producing a CSS bundle with only @font-face rules (33KB)
and zero Tailwind utility classes. The UI rendered as unstyled HTML
(black background, white text, no spacing).

- Add web/postcss.config.mjs wiring @tailwindcss/postcss (matches the
  pattern used by sibling repos like ChronoMind)
- Copy postcss.config.mjs into the web Docker build stage so 'pnpm run
  build' can resolve it

web/Dockerfile

@@ -17,6 +17,7 @@ RUN pnpm install --ignore-scripts --lockfile=false
 COPY web/next.config.ts ./next.config.ts
 COPY web/tsconfig.json ./tsconfig.json
 COPY web/next-env.d.ts ./next-env.d.ts
+COPY web/postcss.config.mjs ./postcss.config.mjs
 COPY web/src/ ./src/
 COPY shared/ ../shared/
 

web/postcss.config.mjs

@@ -0,0 +1,7 @@
+const config = {
+  plugins: {
+    "@tailwindcss/postcss": {},
+  },
+};
+
+export default config;