fix: remove duplicate password checks and UI rendering in SignUp

[Vaanshimadaan]

Description

Please include a summary of the changes and the rationale behind them. Reference any files, components, or modules modified.

• Summary of changes: Removed the duplicate passwordChecks mapping and UI rendering block that was accidentally pasted twice inside the component.
• Rationale: The duplicate block was causing block-scoped variable conflicts, duplicate key warnings in the console, and visual layout glitches in the browser. Cleaning this up ensures the code compiles successfully and looks correct.
• Modified files/components: src/components/SignUp.tsx

Fixes #283

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (structural code cleanups with no behavior changes)
• Performance improvement (indexing speed, search latency, UI responsiveness)
• Documentation update (non-executable reference upgrades)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings or console errors
• I have run tests locally (pnpm run test or vitest run under backend/) and they pass
• Any dependent changes have been merged and published in downstream modules

Verification Details

Please describe the tests or manual steps that you ran to verify your changes. Provide instructions so we can reproduce.

1. Test case / steps:
   • Run the local development server and navigate to the SignUp registration page.
   • Enter a password in the password field to trigger the real-time strength validation.
2. Expected result:
   • The password requirement criteria (Length, Number, Uppercase) display cleanly exactly once.
   • The validation rules update dynamically as you type without generating any duplicate key errors or warnings in the browser console.

Visual Documentation

If this PR introduces visual or layout modifications (frontend changes), please attach screenshots or screen recordings showing before/after comparison.