Fix submission metrics category breakdown

[JoaquinBN]

Summary

• keep category page backgrounds white across dashboard routes
• add community/category coverage to submission analytics filters
• show per-category metric rows when viewing all categories
• exclude onboarding and social-linking awards from points-awarded metrics

Verification

• npm run build
• npm test -- categoryTheme.test.js
• ./env/bin/python -m py_compile contributions/tests/test_canceled_submissions.py contributions/views.py

Note: Django test execution is blocked locally by the existing test database seed issue in migration 0037_seed_featured_content, which expects albert@genlayer.foundation.