[0.7] A2A agent identity (agent: namespace + DPoP-bound)

[Raulgooo]

Release

0.7 — A2A Auth Layer

Objective

Agents have DPoP-bound identities for A2A calls.

Problem

• No A2A identity standard
• Agents reuse human auth patterns

Fix

1. A2A agent identity using agent: namespace
2. DPoP-bound identity tokens
3. Identity registration endpoint
4. Identity introspection

Files

• internal/api/a2a_handlers.go (new)
• internal/auth/a2a.go (new)
• internal/storage/a2a.go (new)

Acceptance Criteria

• A2A identity registration
• DPoP-bound identity token
• agent: namespace
• Identity introspection
• SDK support