Matter/client structure polish

From the PR description

Summary

• Rename user-facing Projects/Project labels to Matters/Matter across navigation, breadcrumbs, overview, pickers, and workflow/review modals while leaving /projects routes and MikeProject API types intact.
• Update uploaded file/list language to Documents, including empty states and upload actions.
• Clarify matter-first flow with copy for creating or choosing a matter, uploading documents, and asking Gary cited questions.
• Fix frontend/package-lock.json so @fontsource/inter@5.2.8 is locked and npm ci works again.

Validation

• npm install: PASS; updated package-lock.json only.
• npm ci: PASS.
• npm run build: raw command still fails without Supabase env because /account/models prerender requires NEXT_PUBLIC_SUPABASE_URL; with placeholder env vars from .env.local.example, build PASS.
• npm run lint: FAILS on pre-existing repo-wide ESLint issues unrelated to this lockfile/copy change, including react-hooks/set-state-in-effect, no-explicit-any, react/no-unescaped-entities, react-hooks/static-components, and no-require-imports.

Notes

• Backend files not touched.
• API routes, internal project identifiers, database-facing fields, imports, and /projects URLs intentionally left unchanged.
• No Bun, pnpm, or Yarn lockfiles were found or added.