Align project dependencies and cleanup stale branches

[BigSimmo]

Summary

• update direct dependencies to current compatible releases and align React/React DOM at 19.2.7
• add scoped audit overrides for PostCSS, tmp, and uuid while preserving ExcelJS spreadsheet support
• document stale branch audit and remove superseded local/remote branches
• update PDF.js document viewer loading for pdfjs-dist 6 and isolate the repo-wide Prettier pass in a separate commit

Verification

• npm ls --depth=0
• npm audit
• npm outdated (only ESLint 10 remains intentionally deferred because eslint-config-next peers on ESLint 9)
• npm run typecheck
• npm run lint
• npm test
• npm run build
• npm run format:check
• npm run check:supabase-project
• git diff --check HEAD --
• npm run ensure plus /api/local-project-id verification
• browser QA: dashboard and /documents/315519ff-e018-46f5-8109-1ac56e736431