Fix applyRange plus sign at zero

[unrealdreamz]

Fixes #1412

Summary

• Stop preserving a leading + when ranged item text resolves exactly to zero.
• Add an applyRange regression for a signed range centered on zero.

Root Cause

itemLib.applyRange preserved the original plus sign when the interpolated range value was >= 0. That produced +0 ... for ranges that land exactly on zero, even though the rest of item text formatting uses plain 0.

Fix

Preserve + only for strictly positive interpolated values. Negative values already drop the plus sign, and now zero does too.

Validation

• git diff --check - pass, exit code 0.
• Targeted regression added in spec/System/TestItemTools_spec.lua.
• Docker/Busted not run locally in this pass because this machine was explicitly kept free of local test/container windows; GitHub Actions should run the normal suite on the PR.

Risk/Rollback

Very low risk: the change is limited to signed range formatting when an originally plus-prefixed range resolves to exactly zero.

[LocalIdentity]

Does not work, currently just hides the slider now