Fix UI dependency CVEs for uuid and marked

Summary

Fixes the UI dependency CVEs mirrored as GitHub issues:

• https://github.com/postgres-ai/database-lab-engine/issues/346 — CVE-2026-41907 in uuid@8.3.2, fixed by forcing uuid >=14.0.0
• https://github.com/postgres-ai/database-lab-engine/issues/347 — CVE-2026-41680 in marked@14.0.0, fixed by forcing marked >=18.0.2

Also relates to GitLab work item #706 (closed).

Changes

• Adds pnpm overrides for vulnerable transitive dependency ranges.
• Regenerates ui/pnpm-lock.yaml with pnpm 8.15.9, preserving lockfile v6.

Validation

Red/green:

• RED: grep -qE '^ /(uuid@8\.3\.2|marked@14\.0\.0):' ui/pnpm-lock.yaml found both vulnerable versions before the fix.
• GREEN: same lockfile check passes after the fix.

Local gates:

• PATH=/tmp/pnpm-bin:$PATH pnpm --filter @postgres.ai/ce lint
• PATH=/tmp/pnpm-bin:$PATH pnpm --filter @postgres.ai/ce build
• PATH=/tmp/pnpm-bin:$PATH pnpm --filter @postgres.ai/ce test
• PATH=/tmp/pnpm-bin:$PATH pnpm --filter @postgres.ai/ce cy:run

All passed locally.