Add DEVELOPER_FOLLOWUP_ROADMAP.md with actionable engineering tasks (#12)

Created developer-focused roadmap that decomposes high-level strategic
goals from ROADMAP.md into concrete, implementable tasks with technical
specifications.

## Document Structure

- **Immediate Action Items (Phase 1)** - Remaining 5% to complete:
security audit workflow, API Gateway implementation, Docker/K8s/CI-CD
setup, monitoring stack, missing frontend screens
- **Phase 2 Technical Specs** - DeFi contracts (staking, AMM, farming),
referral system, NFT marketplace, i18n implementation with code examples
and function signatures
- **Technical Debt** - Code quality checklist, security hardening
(reentrancy guards, rate limiting, secrets management), gas and
performance optimization strategies
- **Infrastructure** - Database scaling (replication, sharding), K8s
migration, CDN integration
- **Testing Framework** - Smart contract unit/integration tests, backend
load testing, frontend E2E flows with coverage targets
- **Documentation Matrix** - API specs (Swagger), architecture diagrams,
deployment runbooks, disaster recovery procedures
- **Developer Experience** - Onboarding checklist, sprint planning
template, KPI tracking, escalation paths

## Key Additions

Provides concrete artifacts developers can pick up immediately:
- Smart contract function signatures and gas optimization notes
- API endpoint definitions with request/response schemas
- File paths for new components (`/server/routes/api.js`,
`/contracts/ZeaStaking.sol`)
- Testing coverage targets and tool recommendations
- CI/CD workflow configurations (GitHub Actions YAML structure)

Bridges gap between "what to build" (ROADMAP.md) and "how to build it"
with implementation-ready specifications.

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<details>

<summary>Original prompt</summary>

> DEVLEOPER FOLLOWUP ROADMAP.md


</details>



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Author: cvsz