docs: Public roadmap & RFC/ADR index (ROADMAP.md)

[joelpeace48-cell]

Background & current state

There are RFCs/ADRs (docs/rfcs, docs/adr) and now a large set of epics/issues, but no single public roadmap tying direction together — useful for contributors and grant reviewers to see vision + progress.

Goal

Author ROADMAP.md linking the epics (ZK, token/payouts, account abstraction, indexer, scale, SRE, security, anti-sybil, gamification, multi-tenancy, DX, mobile, analytics, testing, docs), open RFCs/ADRs, and milestones.

Outline

• Vision + themes; epic summaries with links to tracking issues/labels; milestones (testnet → hardening → mainnet); how to propose changes (RFC process); link from README.

Task breakdown

• Write ROADMAP.md mapping epics → issues/labels.
• Link RFCs/ADRs + milestones.
• Keep it current via a label/milestone convention.

Acceptance criteria

• Roadmap reflects the epics + open RFCs/ADRs with working links.

Verification

• Links resolve; maintainer review.

Difficulty: easy · Effort: S–M · documentation