Fix build issues found during Docker validation

- Dockerfile: add COPY db/ /app/db/ so migrations are available at
  runtime (server/src/db.js requires ../../db/migrations at startup)
- vite.config.js: fix dev proxy port from 3001 to 3000 to match
  server's default PORT

Docker build passes; server starts and connects to DB correctly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -19,6 +19,9 @@ RUN npm install --omit=dev
 
 COPY server/ ./
 
+# Copy db migrations (required by server/src/db.js at runtime)
+COPY db/ /app/db/
+
 # Copy built client assets
 COPY --from=client-build /app/client/dist /app/client/dist