Prepare RelayOS public alpha launch

[rufatixx]

What changed

• redesigned the README first screen with an original RelayOS social card and an explicit simulator-only scope
• added a one-command .NET console simulation for Alice → Courier → Bob
• replaced the stock .NET app artwork with an original RelayOS mark and documented the Open Sans license
• installed the complete AGPL-3.0 license text and corrected the stale MIT contribution notice
• added alpha package metadata, a package-safe README, changelog, citation, release notes, support, conduct, ownership, and issue-routing files
• expanded CI to run the simulator, audit dependencies, pack RelayOS.Core, and upload the package artifact

Why

RelayOS had strong Core code but an empty public GitHub profile, no release framing, no low-friction demo, inconsistent licensing, and template branding. This prepares an honest, credible first alpha and gives visitors a clear contributor path.

User and developer impact

Visitors can understand the project scope immediately and run the complete local simulation with one command. Contributors get discussions, bounded issues, ownership and conduct guidance, and a validated package artifact.

Validation

• 27/27 Core tests pass on .NET 10
• the console simulation encrypts, persists, forwards, and decrypts a packet successfully
• NuGet audit reports no vulnerable dependencies
• RelayOS.Core 0.1.0-alpha.1 packs successfully
• XML, YAML, staged diff, and credential-pattern checks pass

Remaining limits

The transport is still an in-process simulator. The MAUI Android source demo is not built by Core CI, and this PR does not claim Bluetooth, Wi-Fi Direct, mesh networking, production readiness, or an independent security audit.