fix(tui): show model search input

[WqyJh]

Summary

• keep the filter input visible when a dialog uses external filtering via onFilter
• restores search in /models, where DialogModel already handles filtering but passed skipFilter
• add a focused test for the filter-input visibility rules

Fixes XiaomiMiMo#487

Tests

• npx -y bun@1.3.11 test test/tui/dialog-select.test.ts --timeout 30000
• npx -y bun@1.3.11 typecheck
• git diff --check

---

Mirrored from XiaomiMiMo/MiMo-Code#551 — original author @xiaokhkh.