PR-F: polish product language

[suguanYang]

Summary

• replace visible implementation jargon with non-technical product language
• make source rows use separate accessible controls for include/exclude and opening content sections
• rename visible citation and parsed-section labels to source/content-section language
• make the direct login gate read as Knowhere account sign-in, not Dashboard internals

Verification

• pnpm lint
• pnpm test
• pnpm test:integration
• DATABASE_DRIVER=pg DATABASE_URL=postgres://postgres:postgres@127.0.0.1:55432/knowhere_notebook_e2e DASHBOARD_SESSION_URL=http://dashboard.127.0.0.1.nip.io:3000/api/orpc/users/getCurrentUser DASHBOARD_LOGIN_URL=http://dashboard.127.0.0.1.nip.io:3000/login NOTEBOOK_PUBLIC_URL=http://notebook.127.0.0.1.nip.io:3001 KNOWHERE_API_KEY=sk_placeholder KNOWHERE_BASE_URL=https://api-staging.knowhereto.ai AI_GATEWAY_API_KEY=vck_placeholder pnpm build