feat: add JWT/OAuth2 authentication & multi-tenant federation

- Add LLMAuth struct with support for Bearer, API Key, and Custom auth types
- Implement applyAuth() to inject auth headers into LLM requests
- Add X-Tenant-ID header for multi-tenant isolation
- Add X-OAuth-Scopes header for OAuth2 scope enforcement
- Add UpdateAuth() for runtime token refresh (long-running workflows)
- Update LLMRouterConfig with Auth and TenantID fields
- Document 4 authentication patterns (Bearer, API Key, Custom, Router config)
- Add security best practices: token vault integration, tenant isolation, scopes
- Add audit headers for compliance & logging
- Create multi-tenant router factory pattern

Auth types supported:
- Bearer: JWT/OAuth2 tokens (most secure for federated access)
- API Key: Static keys (X-API-Key header)
- Custom: Any custom header-based scheme
- None: No authentication

Customers can now pass per-tenant JWT tokens with customized scopes
and isolated LLM API access per tenant/customer.

k8s/git-commit.yaml

@@ -9,6 +9,6 @@ metadata:
     app.kubernetes.io/name: poimen
     app.kubernetes.io/component: orchestrator
 data:
-  GIT_COMMIT: "f3ce019c"  # Updated automatically by CI/CD
+  GIT_COMMIT: "30644a8e"  # Updated automatically by CI/CD
   GIT_BRANCH: "main"
-  DEPLOYMENT_DATE: "2026-09-03"
+  DEPLOYMENT_DATE: "2026-09-04"