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

cmd/mavend/main.go

@@ -340,6 +340,10 @@ func run(args []string) error {
 		// retention loop. Off unless a capture block enables it, in which case
 		// all four capture methods answer ErrUnknownMethod.
 		wireCapture(srv, keeper, st, voiceW, phr, cfg)
+		// Voice identification (Vikunja #255). Enrolment plumbing only until a
+		// speaker-embedding model exists on disk; off entirely without a speaker
+		// block, so no wire path takes a voiceprint on a default box.
+		wireSpeaker(srv, st, cfg)
 	}
 
 	// WrapKeyFn — wraps the env key with a passkey credential public key and
@@ -485,6 +489,10 @@ func run(args []string) error {
 			wireModelSwap(srv, phr, cfg)
 			keeper := wireVision(ctx, srv, st, embedderOf(voiceW), cfg)
 			wireCapture(srv, keeper, st, voiceW, phr, cfg)
+			// Voice identification (Vikunja #255). Enrolment plumbing only until a
+			// speaker-embedding model exists on disk; off entirely without a speaker
+			// block, so no wire path takes a voiceprint on a default box.
+			wireSpeaker(srv, st, cfg)
 
 			// Start voice server.
 			if voiceW != nil {