DX pass: wevm-style polish + agent guide

[mmurrs]

Summary

• Add AGENTS.md as the canonical agent integration guide — CORS, fail-fast config (no || testnet fallbacks), CDP key formats, ASCII description constraint, paymentDescription documented
• Rewrite README in wevm-family voice; drop internal-app references; add explicit Base mainnet section and human-readable link to the agent guide
• Replace domain-specific findmea-migration.js example with a generic migration sketch; tighten minimal-api.js
• Tighten JSDoc and assertion error messages across src/ to consistently name field + env var + fix
• Switch package.json#files to an explicit allowlist; expand keywords (mppx, usdc, base, cdp, agentic, etc.)

No public function signatures changed. No version bump. No new dependencies.

Test plan

• npm run check — typecheck + 13/13 smoke tests pass
• npm pack --dry-run — 14 files, 28.9 kB, no domain-specific examples in tarball
• Skim AGENTS.md cold-read: confirm an agent could integrate dual402 from it without context
• Skim README.md for tone alignment with mppx/wevm

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