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/client.go

@@ -515,6 +515,34 @@ func (c *Client) CaptureStatus(ctx context.Context) (CaptureStatusResp, error) {
 	return r, nil
 }
 
+// EnrollSpeaker registers a voice from several deliberately recorded samples
+// (Vikunja #255). ErrUnknownMethod means no speaker block is configured, which
+// is the default: on an unconfigured box there is no way to take a voiceprint.
+func (c *Client) EnrollSpeaker(ctx context.Context, req EnrollSpeakerReq) (EnrollSpeakerResp, error) {
+	var r EnrollSpeakerResp
+	if err := c.call(ctx, MethodEnrollSpeaker, req, &r); err != nil {
+		return EnrollSpeakerResp{}, err
+	}
+	return r, nil
+}
+
+// ListSpeakers reports who is enrolled. The voiceprints themselves stay in
+// core. Enabled is false when profiles exist but no embedding model is wired,
+// so a surface can say "enrolled, not recognising" rather than implying Maven
+// knows who is talking.
+func (c *Client) ListSpeakers(ctx context.Context) (ListSpeakersResp, error) {
+	var r ListSpeakersResp
+	if err := c.call(ctx, MethodListSpeakers, nil, &r); err != nil {
+		return ListSpeakersResp{}, err
+	}
+	return r, nil
+}
+
+// ForgetSpeaker deletes one voiceprint.
+func (c *Client) ForgetSpeaker(ctx context.Context, id string) error {
+	return c.call(ctx, MethodForgetSpeaker, ForgetSpeakerReq{ID: id}, nil)
+}
+
 // SwapModel asks core to load another resident model (Vikunja #250).
 // ErrUnknownMethod means core has no phraser.swap_models allowlist configured;
 // ErrForbidden means the path is not on it, or step-up was not asserted. A