Add encrypted multiplayer workspaces

[nativ3ai]

Adds ciphertext-only H1DR4 relay support while keeping Sibyl local to every operator.

What ships

• One-command attackgraph host flow with H1DR4 passkey device approval; no shared API secret, wallet, or payment.
• One-use workspace creation grants bound to the requesting client's Ed25519 key.
• One-use encrypted invites and independent revocable member credentials.
• AES-256-GCM workspace snapshots signed per device with Ed25519.
• Automatic pull-before-read and publish-after-write synchronization for MCP tools.
• Host, invite, join, sync, member-list, revoke, and status controls through CLI and MCP.
• Non-blocking MCP hosting: first call returns the approval URL, second call completes after passkey approval.
• Cursor-based idempotent catch-up with offline local Sibyl behavior.
• Production operator guide and two-client relay smoke.

Validation

• 61 pytest tests passed.
• Ruff clean.
• GitHub CI passed.
• CLI host options expose browser and headless approval modes.
• Two isolated Sibyl clients synchronized through the production H1DR4 route.
• Raw relay inspection confirmed that target and finding plaintext were absent.