Clean stale frontend identity and CSS

[BigSimmo]

Summary

• Removes duplicated local-project identity helpers from the dashboard and document viewer by sharing one browser-safe helper.
• Replaces a non-functional Tailwind arbitrary border utility that referenced undefined --accent with the existing --border token.
• Makes no dependency, env, Supabase data, or deployment changes.

Verification

Local verification under Node 22:

• npm run lint passed
• npm run typecheck passed
• npm run test passed: 39 files, 240 tests
• npm run build passed
• npm run test:e2e:chromium passed; Playwright last-run marker reports passed with no failed tests
• git diff --check HEAD -- passed

Known deferrals

• npm run format:check is still a known repo-wide baseline issue and will be fixed in a separate format-only branch.
• npm ls --depth=0 reports transitive optional native/wasm packages as extraneous even after npm ci; this is deferred to a separate npm tree-noise investigation.
• Larger architecture cleanup for ClinicalDashboard.tsx, DocumentViewer.tsx, rag.ts, and oversized tests is intentionally out of scope.

Risk notes

• The branch touches client UI paths, so Chromium e2e was run.
• No ignored files, env files, logs, caches, private data, or generated artifacts were staged.