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/auth/auth_test.go

@@ -442,3 +442,33 @@ func TestRequirement_Capture(t *testing.T) {
 		t.Errorf("voice starting a capture = %v; want allowed", err)
 	}
 }
+
+// TestRequirement_Speaker — a voiceprint is a biometric of a named person, so
+// taking one is step-up: a deliberate act from a surface that can carry a
+// passkey gesture, never something the voice path does mid-conversation.
+//
+// Deletion is one rung lower, and that asymmetry is the point. Everywhere else
+// in the table the destructive direction is gated at least as hard as the
+// constructive one; for a biometric that would be backwards, because getting
+// rid of it must never be the harder half.
+func TestRequirement_Speaker(t *testing.T) {
+	if got := Requirement(ipc.MethodEnrollSpeaker); got != AuthStepUp {
+		t.Errorf("EnrollSpeaker authority = %v; want AuthStepUp", got)
+	}
+	if got := Requirement(ipc.MethodForgetSpeaker); got != AuthWrite {
+		t.Errorf("ForgetSpeaker authority = %v; want AuthWrite", got)
+	}
+	if got := Requirement(ipc.MethodListSpeakers); got != AuthRead {
+		t.Errorf("ListSpeakers authority = %v; want AuthRead", got)
+	}
+	// Voice cannot enrol anybody, however the utterance is phrased.
+	voice := Scope{Surface: SurfaceVoice, Module: "voice", SourceScope: []string{"*"}}
+	if err := Can(ipc.MethodEnrollSpeaker, voice, nil); err == nil {
+		t.Error("voice enrolling a speaker was allowed; want refused")
+	}
+	// But it can read the roster, which is what answering "кого ты знаешь?"
+	// needs.
+	if err := Can(ipc.MethodListSpeakers, voice, nil); err != nil {
+		t.Errorf("voice listing speakers = %v; want allowed", err)
+	}
+}