Fix treasury balance visibility

[Mosas2000]

Changes Made:
Created useTreasuryBalance hook (
useTreasuryBalance.ts
)

Fetches treasury balance from the Stacks API
Provides balance in both micro-STX and STX
Auto-refreshes every 60 seconds
Includes error handling and loading states
Updated CreateProposalForm component (
CreateProposalForm.tsx
)

Added treasury balance display near the proposal form
Integrated real-time validation against treasury balance
Added pre-submit warning when request exceeds available funds
Visual indicators for treasury health status
Updated SPA CreateProposalPage (
CreateProposal.tsx
)

Added treasury balance display
Integrated treasury balance validation
Added warning messages for insufficient funds
Enhanced validation logic (
validation.ts
)

Created validateAmountAgainstTreasury function
Validates proposal amounts against current treasury balance
Provides clear error messages with available balance
Refactored TreasuryBalance component (
TreasuryBalance.tsx
)

Now uses the shared useTreasuryBalance hook
Reduced code duplication
Added comprehensive tests (
validation.test.ts
)

Tests for treasury balance validation
Edge cases for null balance and decimal amounts
All tests passing
Commits (7 total):
add treasury balance hook for fetching contract balance
integrate treasury balance display in proposal form
refactor treasury balance component to use shared hook
add treasury balance validation helper function
add treasury balance display to spa proposal form
export treasury balance hook from hooks index
add tests for treasury balance validation
Acceptance Criteria Met:
✅ Treasury health is visible during proposal drafting
✅ Amount validation mirrors on-chain rules
✅ Users understand why a proposal may be unfundable before they submit it
✅ Balance is synchronized with the same source used by execution flow
✅ Pre-submit warning when request exceeds available funds

Closes #250