fix: add missing retry module for bags api integration

[0xAxiom]

What: Created the missing retry.ts module that was causing import errors

• Implements bagsApiFetch function with proper Bags API base URL handling and headers
• Implements withRetry function with exponential backoff, jitter, and rate limiting awareness
• Adds proper timeout support (30s default) and error handling
• Includes rate limit header extraction utilities for monitoring API usage
• Resolves import errors in file_upload.ts and fee_share_config.ts

Why:

• The dapp-factory files were importing from ./retry.js but this module did not exist
• This was causing runtime import failures when the Bags API integration was used
• Identified during security review by Cipher subagent

Tested:

• TypeScript compilation passes (npm run type-check:dapp)
• No linting errors
• Module properly exports required bagsApiFetch and withRetry functions
• Follows established patterns from other utilities in the codebase

Technical details:

• Uses proper ES module import/export syntax with .js extensions for compatibility
• Implements exponential backoff with jitter to prevent thundering herd problems
• Handles standard HTTP retry scenarios (429, 502, 503, 504, etc.)
• Properly configured for Bags API rate limits (1000 req/hour)
• Includes comprehensive error handling and logging