Improve Cua listing accuracy and focus

[foo-bender]

What changed

• rewrote Cua's short description and body around its differentiated background driver plus cross-OS sandbox/fleet offering
• replaced the unsupported snapshot-reproduction bullet with current documented capabilities
• added current first-party Cua Driver and sandbox architecture sources
• made focus, local-resource, hosted-pricing, and current snapshot/fork limitations explicit

Evidence

• https://cua.ai/cua-driver
• https://cua.ai/docs/concepts/how-sandboxes-work
• https://cua.ai/
• https://github.com/trycua/cua/blob/main/LICENSE.md

All four URLs returned HTTP 200 on 2026-09-26.

Verification

• npm test (84 passed)
• npm run validate:content (16 categories, 49 tools, 1 redirect/retirement)
• git diff --check

No merge or deployment performed.