feat(mcp): expose the platform through Effect MCP

[KingDoxik]

Summary

• replace the minimal MCP protocol frontend with an Effect MCP registry and Cloudflare-safe stateless HTTP adapter
• preserve the focused paywall authoring tools while adding a schema-discoverable gateway over every customer-facing platform RPC
• add operation and live-paywall resources, plus user API key and project secret key authentication
• keep administrative transport extensions outside the customer MCP surface

Why

Effect MCP's stock HTTP transport keeps session state in process memory. Edge requests may reach different Worker isolates, so the endpoint needs to remain stateless while still using Effect MCP for tool/resource registration, schemas, dispatch, and result handling. The previous endpoint also exposed only the paywall authoring subset rather than the broader platform.

Impact

Agents can discover exact operation schemas with platform_describe, invoke existing authorized handlers through platform_call, and continue using the focused paywall tools. Existing service-level authorization remains authoritative for both user and project credentials.

Validation

• pnpm --filter @voidhash/backend test (114 tests)
• pnpm --filter @voidhash/backend typecheck
• complete RPC-catalog contract coverage
• HTTP-level stateless initialize/call and authentication coverage
• publication-boundary checks

[github-actions]

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