feat: generate barrel index.ts for multi-contract sync

[satoshai-dev]

Summary

• After abi-cli sync, generates an index.ts barrel file that re-exports all ABIs
• Export names derived from name alias (or contract name), converted to camelCase with Abi suffix
• Only generated for ts format (skipped for json)

Closes #20

Example

Config:

{
  "outDir": "./abis",
  "contracts": [
    { "id": "SP102...amm-pool-v2-01", "name": "amm-pool" },
    { "id": "SP2PA...nft-trait" }
  ]
}

Generated abis/index.ts:

export { abi as ammPoolAbi } from './amm-pool.js';
export { abi as nftTraitAbi } from './nft-trait.js';

Test plan

• toCamelCase conversion (kebab-case, camelCase, single word, with numbers)
• generateBarrel output format and sorting
• Sync generates index.ts for ts format
• Sync skips barrel for json format
• Barrel uses name alias when available
• All 82 tests pass, typecheck and lint clean

🤖 Generated with Claude Code