Add meeting capture with explicit start and stop (#253)

Maven can record a meeting when she is told to, transcribe it through the
STT she already has, and write a summary note. The audio lives in the blob
store #252 introduced, under the same retention loop.

Nothing here listens. Recorder.Append is the only way audio enters and it
refuses every frame unless someone explicitly started a session, so audio
arriving at an idle core is dropped rather than buffered. The plan document
asked for a keyword trigger ("maven record" heard in the room) and that is
refused: noticing a keyword means listening to the room, which is the one
behaviour this capability must not have.

Off unless configured twice over. No media block means nowhere to keep
audio, no capture block means no recorder, and in either case the four IPC
methods answer ErrUnknownMethod. On an unconfigured box there is no wire
path that begins a recording at all.

A forgotten session ends itself at max_minutes, checked on every append,
and the audio collected before the cap is kept. Stop with discard set is
what "забудь, не записывай" maps to and it leaves nothing behind. The
verbatim transcript is not saved unless save_transcript says so; the
summary is.

Long audio against n_ctx 4096 is handled by map-reduce over 3000-rune
windows rather than by truncation, because a truncated meeting summary
reads as complete and is not. Transcription is windowed at five minutes so
the whisper worker stays responsive to the voice path.

No second STT: internal/capture takes the stt.Transcriber the voice path
already holds. Capture with voice off is refused rather than degraded,
since hours of unreadable audio of other people is worse than no recording.

The three write methods are AuthWrite, not AuthStepUp: step-up needs a
passkey gesture the voice path cannot make, which would leave "запиши
встречу" impossible by voice. capture_status is AuthRead.

make build and make test both pass.

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

internal/ipc/client.go

@@ -473,6 +473,48 @@ func (c *Client) DescribeImage(ctx context.Context, req DescribeImageReq) (Descr
 	return r, nil
 }
 
+// CaptureStart begins recording a meeting (Vikunja #253). ErrUnknownMethod
+// means the operator has not enabled capture — the caller should say so and stop
+// asking, not retry.
+func (c *Client) CaptureStart(ctx context.Context, req CaptureStartReq) (CaptureStartResp, error) {
+	var r CaptureStartResp
+	if err := c.call(ctx, MethodCaptureStart, req, &r); err != nil {
+		return CaptureStartResp{}, err
+	}
+	return r, nil
+}
+
+// CaptureAppend hands one chunk of audio to the running session. An error means
+// the frame was not kept: either nothing is being recorded, or the session hit
+// its time limit. Either way the client stops sending.
+func (c *Client) CaptureAppend(ctx context.Context, req CaptureAppendReq) (CaptureAppendResp, error) {
+	var r CaptureAppendResp
+	if err := c.call(ctx, MethodCaptureAppend, req, &r); err != nil {
+		return CaptureAppendResp{}, err
+	}
+	return r, nil
+}
+
+// CaptureStop ends the session. Slow — it transcribes and summarises the whole
+// recording — so pass a context with room. Set Discard to throw the recording
+// away instead.
+func (c *Client) CaptureStop(ctx context.Context, req CaptureStopReq) (CaptureStopResp, error) {
+	var r CaptureStopResp
+	if err := c.call(ctx, MethodCaptureStop, req, &r); err != nil {
+		return CaptureStopResp{}, err
+	}
+	return r, nil
+}
+
+// CaptureStatus reports the running session, if any.
+func (c *Client) CaptureStatus(ctx context.Context) (CaptureStatusResp, error) {
+	var r CaptureStatusResp
+	if err := c.call(ctx, MethodCaptureStatus, nil, &r); err != nil {
+		return CaptureStatusResp{}, err
+	}
+	return r, 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