[Frontend] Consistent amount input validation with inline and accessible errors

[grantfox-oss]

Telegram (ask questions / claim the issue here first): https://t.me/+DOylgFv1jyJlNzM0

Why this matters

Lend and repay compute a precisionError and disable the submit button, but the validation feedback is inconsistent and not always announced to assistive tech. Users see a dead button with no explanation. Amount inputs should validate precision, range, and balance inline.

Acceptance criteria

• Shared amount input that validates precision (via amount.ts), positive range, and available balance
• Inline error text tied to the input with aria-invalid and aria-describedby
• Disable submit only alongside a visible reason
• Reuse across lend, repay, send remittance, and request loan

Files to touch

• src/app/[locale]/lend/LendPageClient.tsx, src/app/[locale]/repay/[loanId]/page.tsx, src/app/[locale]/send-remittance/, src/app/[locale]/request-loan/page.tsx
• src/app/utils/amount.ts
• src/app/components/global_ui/ (shared input)

Out of scope

• Currency conversion display

[Opulencechuks]

I am confident that i can implement this, having worked on similar issues in the past

[extolkom]

hi, please assign me

[grantfox-oss]

🦊 GrantFox — @extolkom has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #20)
2. Your PR will be reviewed by the LabsCrypt maintainers

Good luck! Track your progress on GrantFox.