slice 8C Phase A: agent disk endpoints + data-bearing classifier gate + mkfs (v0.12.0)

internal/storage: mkfs executor (Format, device-pinned, narrow FELHOM_FORMAT
sudoers) + data-bearing device inspection (InspectDevice/DeviceProbe via
blkid+lsblk; conservative — ambiguous=data-bearing). internal/localapi: /disks
(+ data-bearing flag), /disks/assign (EnsureMount), /disks/eject (Unmount +
dependent guests), /disks/format. SECURITY CENTERPIECE: the agent inspects the
device itself; data-bearing format -> ClassStorageWipe gate -> pending_signature
refused; the caller's claim is never trusted. Additive (no controller change yet).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/storage/observe_test.go

@@ -177,6 +177,10 @@ func (f *fakeHostOps) ThinPoolMetadata(_ context.Context, vg, pool string) (floa
 	v, ok := f.metaByPool[vg+"/"+pool]
 	return v, ok
 }
+func (f *fakeHostOps) InspectDevice(_ context.Context, device string) (DeviceProbe, error) {
+	return DeviceProbe{Device: device, Probed: true}, nil
+}
+func (f *fakeHostOps) Format(context.Context, string, string) error { return nil }
 
 func TestObserve_EnrichesSMARTAndThinPoolMetadata(t *testing.T) {
 	api := &fakeStorageAPI{