fix(display): correct negative BigInt rendering in fmtTokenAmount and formatBigInt

[Sertug17]

Summary

Fixes negative token amounts displaying as "-1.-5 ETH" instead of "-1.5 ETH".

Root cause

JavaScript's BigInt % operator preserves the sign of the dividend. For negative value, the fractional part was also negative, producing a - prefix in the fraction string that got concatenated into the output.

Fix

Use absolute value for all fractional arithmetic and prepend the sign explicitly.

Affected files

• app/vibenet/library/explorer.ts fmtTokenAmount
• app/tips/library/format.ts formatBigInt

Testing

fmtTokenAmount(-1_500_000_000_000_000_000n, 18) // was: "-1.-5", now: "-1.5"
fmtTokenAmount(-500_000_000_000_000_000n, 18)   // was: "0.-5",  now: "-0.5"

Closes #66

[vercel]

@Sertug17 is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.

[cb-heimdall]

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[Sertug17]

Hey @montycheese @haardikk21 small display bug fix here, would appreciate a review when you get a chance. Happy to adjust if anything looks off.