fix(docker): copy source.config.ts into web deps stage (MUL-2649)

apps/web postinstall runs fumadocs-mdx, which reads
apps/web/source.config.ts. The deps stage only copied
package.json files, so `pnpm install --frozen-lockfile`
failed with "Could not resolve /app/apps/web/source.config.ts"
and blocked the GHCR multica-web image build in the v0.3.7 release.

Co-authored-by: multica-agent <github@multica.ai>

Dockerfile.web

@@ -8,6 +8,8 @@ WORKDIR /app
 # Copy workspace config and all package.json files for dependency resolution
 COPY pnpm-lock.yaml pnpm-workspace.yaml package.json turbo.json .npmrc ./
 COPY apps/web/package.json apps/web/
+# postinstall runs fumadocs-mdx which reads apps/web/source.config.ts
+COPY apps/web/source.config.ts apps/web/source.config.ts
 COPY packages/core/package.json packages/core/
 COPY packages/ui/package.json packages/ui/
 COPY packages/views/package.json packages/views/