Ship voice enrolment, and report recognition as blocked (#255)

Maven can now be told who someone is. She cannot yet tell who is speaking,
and this commit is careful to say so rather than pretend otherwise.

What works: profiles are enrolled from several deliberately recorded samples,
listed, and deleted. They live in the existing memory_vectors table under a
"speaker:" id prefix, so there is no migration; what that needed was a wider
interface than memory.Store, hence memory.Catalog with ByPrefix and Delete.
Delete is the load-bearing half — a voiceprint someone asked to be rid of has
to actually go, and a search-only store cannot do that. InMemoryStore.Insert
became an upsert by id to match what the persistent store already did.

What does not work, and why it is not faked: there is no speaker-embedding
model on this box. Sixteen ggufs in /mnt/hdd1/llms, all text; no ECAPA, no
x-vector, no titanet, no wespeaker, no .onnx anywhere under /mnt/hdd1. So
newSpeakerEmbedder returns nil, internal/speaker falls back to
speaker.Disabled, Identify answers ErrDisabled, and the daemon logs which
half is off at startup. The plan's "simple MFCC + GMM" floor is refused in
the package comment: MFCC cosine distance detects channel and loudness as
much as voice, and a biometric that is confidently wrong writes false claims
about named people into his memory. A bad floor is worse than none here.

Refused as well, and the reason is in enroll.go's doc comment: the plan asked
for unknown speakers to be enrolled on first interaction with a TTS "кто
это?". There is no request shape in the protocol that could express that.
Taking a biometric of whoever walks past the microphone does it to guests who
are not party to the exchange, and a synthesised question into a room is not
consent from whoever answers.

Authority: enrolment is AuthStepUp, because it is a deliberate sit-down act
that writes a biometric of a named person and never something done by voice
mid-conversation. Deletion is one rung lower at AuthWrite, deliberately
inverting the usual pattern — getting rid of a biometric must never be the
harder half. Listing is AuthRead and never returns the vectors themselves.

Off unless configured: no speaker block means the three methods answer
ErrUnknownMethod, so a default box has no wire path that takes a voiceprint.

make build and make test pass.

Vikunja #255

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TrVSBKe3RFDF4fGYKWYQnX

internal/ipc/server.go

@@ -473,6 +473,13 @@ type Server struct {
 	CaptureStopFn   CaptureStopFunc
 	CaptureStatusFn CaptureStatusFunc
 
+	// Speaker* — voice identification (Vikunja #255). Set by the daemon only
+	// when a speaker block is configured; nil ⇒ all three methods answer
+	// ErrUnknownMethod, so on an unconfigured box no wire path enrols a voice.
+	EnrollSpeakerFn EnrollSpeakerFunc
+	ListSpeakersFn  ListSpeakersFunc
+	ForgetSpeakerFn ForgetSpeakerFunc
+
 	// UnlockFn — unwraps the store encryption key from the wrapped blob using
 	// the passkey credential public key, opens the encrypted store, and wires
 	// the rest of the daemon (voice, loop, delivery). Set by the daemon when
@@ -510,6 +517,12 @@ type CaptureAppendFunc func(ctx context.Context, req CaptureAppendReq) (CaptureA
 type CaptureStopFunc func(ctx context.Context, req CaptureStopReq) (CaptureStopResp, error)
 type CaptureStatusFunc func(ctx context.Context) (CaptureStatusResp, error)
 
+// EnrollSpeakerFunc / ListSpeakersFunc / ForgetSpeakerFunc — the core-side
+// halves of voice enrolment.
+type EnrollSpeakerFunc func(ctx context.Context, req EnrollSpeakerReq) (EnrollSpeakerResp, error)
+type ListSpeakersFunc func(ctx context.Context) (ListSpeakersResp, error)
+type ForgetSpeakerFunc func(ctx context.Context, req ForgetSpeakerReq) error
+
 // CheckFunc — the auth hook signature. Wired by the daemon (auth.Gate.Check
 // satisfies this); dispatch calls it once per request after param-unmarshal
 // independence (it gets the raw params, may unmarshal what it needs — ipc
@@ -1024,6 +1037,43 @@ func (s *Server) dispatch(ctx context.Context, req Request) (json.RawMessage, er
 		}
 		return nil, fmt.Errorf("%w: %s", ErrUnknownMethod, req.Method)
 
+	case MethodEnrollSpeaker:
+		if s.EnrollSpeakerFn != nil {
+			var p EnrollSpeakerReq
+			if err := unmarshalParams(req.Params, &p); err != nil {
+				return nil, err
+			}
+			resp, err := s.EnrollSpeakerFn(ctx, p)
+			if err != nil {
+				return nil, err
+			}
+			return marshalResult(resp), nil
+		}
+		return nil, fmt.Errorf("%w: %s", ErrUnknownMethod, req.Method)
+
+	case MethodListSpeakers:
+		if s.ListSpeakersFn != nil {
+			resp, err := s.ListSpeakersFn(ctx)
+			if err != nil {
+				return nil, err
+			}
+			return marshalResult(resp), nil
+		}
+		return nil, fmt.Errorf("%w: %s", ErrUnknownMethod, req.Method)
+
+	case MethodForgetSpeaker:
+		if s.ForgetSpeakerFn != nil {
+			var p ForgetSpeakerReq
+			if err := unmarshalParams(req.Params, &p); err != nil {
+				return nil, err
+			}
+			if err := s.ForgetSpeakerFn(ctx, p); err != nil {
+				return nil, err
+			}
+			return marshalResult(nil), nil
+		}
+		return nil, fmt.Errorf("%w: %s", ErrUnknownMethod, req.Method)
+
 	case MethodModelStatus:
 		if s.ModelStatusFn != nil {
 			resp, err := s.ModelStatusFn(ctx)