chore: roll up dependency updates

[atk0309]

Summary

This rollup combines Dependabot PRs #9–#12 on the current main branch so their overlapping backend lockfile changes are tested together.

• Backend: FastAPI 0.141.1, Anthropic 0.120.2, OpenAI 2.50.0, Ruff 0.16.0, httpx2 2.9.1, Uvicorn 0.52.0, and Cryptography 50.0.0
• Frontend: Next.js 16.2.12, Playwright 1.62.0, Biome 2.5.6, and @types/node 26.1.2
• Includes the brace-expansion 2.1.4 security patch through the existing dependency graph and aligns the Biome schema URL with the installed version
• No application behavior, schema, renderer, or production dependency architecture changes

Supersedes #9, #10, #11, and #12.

Validation

• Frozen backend and frontend dependency installs
• node scripts/quality-gate.mjs --fail-on-gap
  • Backend: 328 passed, 13 documented environment-dependent skips
  • Frontend: 342 passed
• Production pnpm build
• pnpm audit --audit-level=low: no known vulnerabilities