Add GitHub Actions badge and topic tags to the repo

[FransDevelopment]

Context

The repo is missing standard open-source discoverability signals that help people find and evaluate the project.

What needs to happen

1. Add status badges to README.md

Add badges at the top of the README showing:

• CI status (manifest compiler workflow)
• npm package version (@open-agent-trust/cli)
• Number of registered issuers (from manifest.json)
• License (MIT)

2. Add GitHub topic tags

Add these topics to the repo settings (Settings → General → Topics):
agent-identity, trust-registry, ed25519, did-resolution, open-standard, ai-agents, attestation, cryptography, zero-trust

3. Add "Used by" section to README

Add a section showing projects that integrate with the registry:

• qntm (encrypted transport)
• ArkForge (execution attestation)
• Agent Passport System (economic authorization)
• Agent Agora (discovery)
• AgentID (identity layer)

Getting started

• The manifest compiler workflow is at .github/workflows/manifest-compiler.yml
• The npm package is @open-agent-trust/cli
• registry/manifest.json has total_issuers for the badge count

Acceptance criteria

• Badges render correctly in the README
• Topic tags are added
• "Used by" section lists current integrations with links