fix: resolve 4 bugs in termui

[saurabhhhcodes]

Description

This PR fixes real bugs found in the codebase:

• Removed redundant boolean comparison: x === true is equivalent to x (and x === false to !x), and shorter to read.
• Replaced global isNaN with Number.isNaN: the global version coerces its argument, so isNaN('1') returns false while Number.isNaN is strict.
• Prevented interval leak: repeated mounts now clear the previous interval before scheduling a new one.
• Removed redundant boolean comparison: x === true is equivalent to x (and x === false to !x), and shorter to read.

Type of Change

• Bug fix (non-breaking change fixing an issue)

How Has This Been Tested?

• Local manual testing

Checklist

• My code follows the style guidelines
• I have performed a self-review

Related Issue

Ref: #3639

Summary by CodeRabbit

• Bug Fixes
  • Improved weather example refresh handling to prevent duplicate refresh timers and maintain consistent five-second updates.
  • Improved rendering reliability so interface updates continue when content is marked for refresh.
  • Strengthened prompt choice validation to handle invalid numeric selections more accurately.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 8f9634f3-573e-46fa-891e-f897de5e8db8

📥 Commits

Reviewing files that changed from the base of the PR and between 6c7584e and 3e7f7a0.

📒 Files selected for processing (3)

• examples/weather/src/index.tsx
• packages/core/src/app/App.ts
• packages/ui/src/prompts.ts

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📝 Walkthrough

Walkthrough

The changes manage the weather refresh interval, broaden render-loop rescheduling for truthy dirty states, and use Number.isNaN for prompt choice validation.

Changes

Weather timer management

Layer / File(s)	Summary
Refresh timer lifecycle examples/weather/src/index.tsx	The refresh timer clears window.__interval before assigning a new 5-second interval that calls fetchWeather.

Render scheduling

Layer / File(s)	Summary
Dirty-state rescheduling packages/core/src/app/App.ts	Post-render scheduling now runs when _rootWidget.isDirty is truthy.

Prompt validation

Layer / File(s)	Summary
Choice NaN validation packages/ui/src/prompts.ts	Choice validation now uses Number.isNaN instead of the coercing global isNaN.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• Karanjot786/TermUI#3421: Overlaps with the weather interval-management change.
• Karanjot786/TermUI#3477: Overlaps with the weather interval and prompt validation changes.
• Karanjot786/TermUI#3601: Overlaps with the Number.isNaN prompt validation change.

Suggested reviewers: karanjot786

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the fixes but omits required package, GSSoC, checklist, and reviewer sections, and does not use the required issue-closing format.	Add all required template sections, complete the checklist, identify the affected packages, and change Ref: #3639 to `Closes `#3639.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies a bug-fix change and follows the required type: short description format.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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