fix(docker): exclude node deps and dist from build context (#949)

Root .dockerignore did not exclude local dependency folders, so
COPY ui/web/ . shipped ui/web's local install into the web-builder
stage. Stale artifacts (e.g. leftover rollup@4.57.1 from older vite@6)
then overrode the result of `pnpm install --frozen-lockfile`,
breaking the musl build on Alpine with:

  Cannot find module @rollup/rollup-linux-arm64-musl

Add explicit ignores for ui/web dependency and dist folders plus a
catch-all for any nested dep folder so Docker builds are
deterministic and match CI regardless of local dev state. Also
speeds up build context transfer.

.dockerignore

@@ -19,5 +19,8 @@ tmp/
 ui/desktop/
 ui/simple-saas/
 !ui/web/
+ui/web/node_modules/
+ui/web/dist/
 plans/
 skills-store/
+**/node_modules/