fix: resolve 4 bugs in termui

[saurabhhhcodes]

Description

This PR fixes real bugs found in the codebase:

• Prevented interval leak: repeated mounts now clear the previous interval before scheduling a new one.
• Added rejection handler to Promise.all: an unhandled rejection in any input promise previously crashed silently.
• Simplified empty-string validation: comparing trim() to '' misses whitespace-only input; .trim().length === 0 is explicit.
• Added Number.EPSILON to Math.round: prevents floating-point drift (e.g. 1.005 * 100 rounding to 100 instead of 101).

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: #3530