**Critical Model References**: Fixed all incorrect and non-existent database model usage across the backend that could cause runtime crashes
  - Fixed `models.walletTransaction` → `models.transaction` in staking system (4 occurrences)
  - Fixed `models.kyc` → `models.kycApplication` in user export functionality
  - Fixed `models.blockchainTransaction` references in 18 NFT-related files
  - Fixed `models.nftIpfsUpload` crash in IPFS service with null check
  - Fixed `models.nftMetadataBackup` crashes in metadata backup service (4 occurrences)
  - All incorrectly referenced models now properly handled with null checks or correct model names

### Staking System

- **Transaction Recording**: Fixed staking position creation failing with "Cannot read properties of undefined (reading 'create')" error
  - Root cause: Attempting to use non-existent `walletTransaction` model
  - Now correctly uses `transaction` model with proper STAKING transaction types
  - Affected endpoints:
    - Staking position creation (`/staking/position`)
    - Staking reward claims (`/staking/position/[id]/claim`)
    - Admin bulk position updates (`/admin/staking/position/bulk`)
- **Audit Trail**: All staking operations now properly create transaction records for complete audit history
- **Metadata Format**: Fixed metadata not being stringified - now properly uses `JSON.stringify()`

### NFT Marketplace

- **Blockchain Transaction Tracking**: Fixed NFT operations not recording blockchain transactions
  - Auction bids now record `NFT_AUCTION_BID` transactions
  - Auction settlements record `NFT_AUCTION_SETTLE` transactions
  - NFT purchases record `NFT_PURCHASE` transactions with full fee breakdown
  - NFT transfers record `NFT_TRANSFER` transactions
  - All transactions include blockchain details (transaction hash, gas, block numbers)
- **Admin Profit Recording**: Fixed NFT marketplace fees not being tracked as admin profits
  - Offer confirmations now create both transaction and adminProfit records
  - Marketplace fees properly linked to profit tracking system
  - Supports multiple currencies with wallet-based tracking
- **Optional Features**: Services gracefully handle missing optional models (IPFS upload tracking, metadata backup)

### Payment Gateway Metadata

- **Metadata Stringification**: Fixed 19 payment gateway files with non-stringified metadata
  - All metadata fields now properly use `JSON.stringify()` before database storage
  - Prevents data corruption and ensures proper JSON parsing on retrieval

### ICO Vesting System

- **Vesting Release Model**: Created missing `icoTokenVestingRelease` model for tracking individual vesting releases
  - Enables proper recording of each scheduled token release
  - Tracks release status (PENDING, RELEASED, FAILED, CANCELLED)
  - Records blockchain transaction hashes for on-chain releases
  - Supports failure tracking with detailed error reasons

## Added

### Database Models

- **NFT Price History Model**: New `nftPriceHistory` model for tracking NFT sale prices over time
  - Records sale price, currency, and USD conversion at time of sale
  - Tracks sale type (DIRECT, AUCTION, OFFER)
  - Links to buyer, seller, token, and collection
  - Enables historical price analysis and floor price tracking
  - Includes blockchain transaction hash reference

- **ICO Token Vesting Release Model**: New `icoTokenVestingRelease` model
  - File: `backend/models/ext/ico/icoTokenVestingRelease.ts`
  - Tracks individual scheduled releases within a vesting plan
  - Fields:
    - `vestingId` - Parent vesting record reference
    - `releaseDate` - Scheduled release date
    - `releaseAmount` - Token amount to release
    - `percentage` - Percentage of total vesting
    - `status` - PENDING | RELEASED | FAILED | CANCELLED
    - `transactionHash` - On-chain transaction hash
    - `releasedAt` - Actual release timestamp
    - `failureReason` - Error details if failed
  - Includes database indexes for efficient queries
  - Properly associated with parent `icoTokenVesting` model

### Transaction Types

- **NFT Transaction Types**: Added 8 new transaction types to support NFT marketplace operations
  - `NFT_PURCHASE` - Direct NFT purchases
  - `NFT_SALE` - NFT sales (seller receiving payment)
  - `NFT_MINT` - NFT minting operations
  - `NFT_BURN` - NFT burning operations
  - `NFT_TRANSFER` - Direct NFT transfers between users
  - `NFT_AUCTION_BID` - Auction bid placements
  - `NFT_AUCTION_SETTLE` - Auction settlements
  - `NFT_OFFER` - Offer-based purchases
- **Admin Profit Types**: Added 3 NFT-related admin profit types
  - `NFT_SALE` - Marketplace fees from direct sales
  - `NFT_AUCTION` - Fees from auction settlements
  - `NFT_OFFER` - Fees from offer acceptances

## Improved

### Transaction Recording

- **Wallet Integration**: All NFT marketplace transactions now properly link to user wallets
  - Enables accurate balance tracking across all transaction types
  - Supports multi-currency operations
  - Gracefully handles cases where wallets don't exist yet

### Code Quality

- **Error Handling**: Enhanced error handling for optional model features
  - IPFS upload tracking gracefully disabled if model not created
  - Metadata backup service continues operation without model
  - Gas history tracking properly guarded with null checks
  - System backup functionality safely disabled when model unavailable

### Model Associations

- **ICO Vesting Relationships**: Enhanced `icoTokenVesting` model with complete associations
  - `hasMany` relationship with `icoTokenVestingRelease` (as "releases")
  - `belongsTo` relationship with `icoTransaction` (as "transaction")
  - `belongsTo` relationship with `user` (as "user")
  - `belongsTo` relationship with `icoTokenOffering` (as "offering")
  - Enables efficient queries with proper eager loading