adapters: openai is a static-key vendor

One registry line — `"openai": StaticKey`. The generic static-key adapter
already serves any vendor (accept is the vendor-independent seal, deliver is the
value unchanged, and refresh/identity/usage are not implemented), so a second
static-key vendor is data, not code. The shape-selection test now asserts
For("openai") reports static-key.

Claude-Session: https://claude.ai/code/session_01LrgweAeERJYBg88c5cKDzF

internal/licences/adapters/adapters.go

@@ -167,6 +167,7 @@ type UsageRow struct {
 var registry = map[string]Shape{
 	"anthropic":         RefreshableGrant,
 	"anthropic-api-key": StaticKey,
+	"openai":            StaticKey,
 }
 
 // For returns the adapter for a vendor, refusing an unknown one clearly.