fix(cua): fall back to clipboard paste on type failures

[danielgwilson]

Summary

• add a clipboard-paste fallback when the E2B desktop write/type method fails
• transfer typed text through a sandbox temp file instead of shell-quoting it into commands
• keep raw typed text out of trace/action labels and command strings

Validation

• pnpm exec vitest run tests/e2b-desktop-executor.test.ts
• pnpm typecheck
• pnpm exec vitest run tests/e2b-desktop-executor.test.ts tests/computer-use.test.ts tests/cua-actor-lab.test.ts
• pnpm build
• pnpm public-surface:scan
• git diff --check