fix(terminal): disable local echo on alternate screen

[ZacharyZcR]

Summary

• bypass local echo prediction while an alternate-screen application is active
• reset pending predictions when entering the alternate screen
• limit rollback erasure to the predicted cells instead of erasing the rest of the line

Verification

• npx vitest run --project frontend src/ui/lib/terminal-local-echo.test.ts
• npx prettier --check src/ui/lib/terminal-local-echo.ts src/ui/lib/terminal-local-echo.test.ts src/ui/features/terminal/Terminal.tsx
• npm run type-check

Fixes Termix-SSH/Support#1230