fix: patch dist ESM import extensions

[peterxing]

Summary

Fixes #2 by making the published dist/ Node ESM-compatible after TypeScript emits extensionless relative imports.

Changes:

• add a post-tsc dist rewrite that appends .js to relative import / export ... from / dynamic import() specifiers when the emitted target exists
• also rewrites .d.ts relative specifiers so published declarations match the runtime JS specifiers
• replace the POSIX-only rm -rf dist clean command with a tiny Node clean script
• keep source imports unchanged, so this is a minimal packaging fix rather than a repo-wide NodeNext migration

Verification

• corepack pnpm install --frozen-lockfile --ignore-scripts
• corepack pnpm run typecheck
• corepack pnpm run build
• corepack pnpm run test:unit — 25 files / 230 tests passed
• corepack pnpm exec prettier --check package.json scripts/clean.mjs scripts/fix-esm-imports.mjs
• corepack pnpm exec eslint scripts/clean.mjs scripts/fix-esm-imports.mjs
• git diff --check
• package self-import smoke after build:
  • import('@goatnetwork/agentkit') -> 162 exports
  • import('@goatnetwork/agentkit/core') -> 21 exports
  • import('@goatnetwork/agentkit/providers') -> 3 exports
  • import('@goatnetwork/agentkit/plugins') -> 129 exports

Note: full pnpm run lint still reports the existing repo-wide warnings plus an existing unused beforeEach error in tests/unit/x402-merchant.test.ts; the touched scripts lint cleanly.