Fix 4 issues: emergency pause controls, blacklist controls, and verif…

[anonfedora]

Fix 4 dashboard and mobile app issues

This PR implements emergency controls and moderation features while verifying existing autocomplete and APY configuration functionality.

Changes

Dashboard - Yield Page (#599)

• Added emergency pause/resume toggle buttons with prominent crimson highlights
• Implemented double-confirmation drawer requiring two explicit validations
• Triggers transaction signing via Freighter to freeze/restore vault operations
• Clear warnings about impact: blocks deposits, withdrawals, halts yield accrual

Dashboard - Contracts Page (#592)

• Added blacklist controls to revoke or suspend usernames
• Implemented confirmation drawer with admin role guards
• Signs blacklist action via Freighter with administrator keys
• Clear warnings about irreversible nature of blacklisting
• Added Actions column to usernames table with blacklist buttons

Mobile App - Transfer Screen (#564)

• Verified existing autocomplete implementation with debounced search (350ms)
• Dynamic queries as users type with dropdown display of matching users
• Backend API integration for username search already functional

Dashboard - Yield Page (#595)

• Verified existing APY configuration page for admin adjustment
• Input forms with validation already implemented
• Freighter client wrapper for on-chain parameter changes already functional

Files Modified

• dashboard/app/dashboard/yield/page.tsx - Emergency pause controls
• dashboard/app/dashboard/contracts/page.tsx - Blacklist controls

Closes #564
Closes #599
Closes #592
Closes #595

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[ONEONUORA]

Great job @anonfedora