Refresh README, docs, and Codex workflows

[TheSilkky]

Summary

• refresh the web-client README to follow the current Proofline repository baseline and source-of-truth map
• align docs with website governance/public-voice sources and current server-backed web-client boundaries
• update reusable Codex prompts with current source-of-truth, validation, sensitive-data, and docs-only workflow guidance
• clarify that server-supported account second-factor routes remain outside the current web-client UI and API-client method surface
• refresh vulnerable lockfile resolutions for vite and transitive undici so the CI dependency audit passes

Validation

• npm ci
• npm run audit
• npm run typecheck
• npm run lint
• npm run test
• npm run build
• npm run test:e2e
• npx prettier --check README.md AGENTS.md SECURITY.md CHANGELOG.md docs/*.md codex/*.md codex/prompts/*.md
• git diff --check

Security and scope notes

• Application source, route behavior, auth/session behavior, and CI workflow files are unchanged.
• Runtime-impacting dependency changes are limited to lockfile patch updates for the CI audit findings: vite 8.0.15 to 8.0.16 and transitive undici 7.26.0 to 7.28.0.
• Preserves web-client boundaries: no recording/capture, browser decryption, key escrow, notification delivery, hosted billing, public admin/operator surface, mobile-client behavior, or production-readiness claims.
• Keeps backend facts tied to open-proofline/server and project-level public governance/voice tied to open-proofline/website.

Closes #77