feat: upload audio, get a private Swedish transcript, discuss it (#33, ADR-033) (#39)

Upload a recording (audio, or video with the camera off), get a private Swedish transcript, and chat about it.

- ADR-033: RLS-scoped private transcript store; ffprobe/ffmpeg intake; gateway transcription (iguana kb-whisper, berget fallback); in-process single-replica worker; chat over the transcript (local models only).
- ADR-034: optional two-engine mode (pianissimo + kb-whisper) reconciled by a LOCAL model; off unless TAPIR_RECONCILE_BASE_MODEL is set.
- ADR-035: real progress (phases, running/quiet/lost), phase logging, every judged spot stored, merged segments.
- Hardening from four adversarial reviews: errors logged and stored as kinds never text; per-engine deadlines; converted-length check; bounded queue; client hang-ups are not errors; strict local-alias check.
- Dockerfile: static ffmpeg/ffprobe 7.0.2 pinned by sha256 (#34). Built and inspected by hand; CI does not build the image on a PR, so its first CI build is this merge.

Uploads stay OFF until TAPIR_UPLOADS_ENABLED is set in the deployment.

Closes #33, #34, #42, #43, #44.

Co-authored-by: Mathias <mthbqv@gmail.com>

internal/adapters/audio/ffmpeg.go

@@ -0,0 +1,62 @@
+package audio
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"os/exec"
+	"strconv"
+	"strings"
+)
+
+// FFmpeg converts any audio container to the strict format whisper wants: 16 kHz
+// mono signed 16-bit PCM WAV (ADR-033). It ALWAYS transcodes, even when the input
+// already is that format — a Teams export often is, and the transcode is then
+// nearly free; assuming it would be the bug. This replaces whisper-server's
+// --convert, whose --tmp-dir is created at process start and rots under macOS
+// periodic cleanup.
+type FFmpeg struct {
+	// Bin is the ffmpeg executable ("ffmpeg" resolves via PATH).
+	Bin string
+	// MaxSeconds caps the converted length when positive. The duration limit is a claim
+	// in the file's header and can be lied about (a 2 h file claiming 10 s converted to a
+	// 120-minute WAV); this bounds what a lie can cost. A minute of slack is added so a
+	// file at the limit is never cut, and the worker measures the result.
+	MaxSeconds int
+}
+
+// lengthSlackSeconds is added to MaxSeconds so ffmpeg's rounding never clips a file that
+// is really at the limit.
+const lengthSlackSeconds = 60
+
+// ToWAV writes src, converted, to dst. Video streams are dropped (-vn): by now the
+// file has already been probed as audio-only, but a cover-art stream must not end
+// up in the WAV.
+func (f *FFmpeg) ToWAV(ctx context.Context, src, dst string) error {
+	bin := f.Bin
+	if bin == "" {
+		bin = "ffmpeg"
+	}
+	// Input restrictions go BEFORE -i: placed after it they would apply to the output.
+	args := append([]string{"-y", "-v", "error"}, inputRestrictions...)
+	args = append(args, "-i", src, "-vn", "-ac", "1", "-ar", "16000", "-c:a", "pcm_s16le")
+	if f.MaxSeconds > 0 {
+		// After -i: an OUTPUT cap. Before it, it would limit what is read, not written.
+		args = append(args, "-t", strconv.Itoa(f.MaxSeconds+lengthSlackSeconds))
+	}
+	args = append(args, "-f", "wav", dst)
+	cmd := exec.CommandContext(ctx, bin, args...)
+	cmd.WaitDelay = killGrace
+	if out, err := cmd.CombinedOutput(); err != nil {
+		if ctxErr := ctx.Err(); ctxErr != nil {
+			return fmt.Errorf("audio: ffmpeg: %w", ctxErr)
+		}
+		return fmt.Errorf("audio: ffmpeg: %w: %s", err, strings.TrimSpace(string(out)))
+	}
+	// A zero exit that wrote nothing is still a failure: never hand whisper a
+	// missing file and let the error surface three layers later.
+	if info, err := os.Stat(dst); err != nil || info.Size() == 0 {
+		return fmt.Errorf("audio: ffmpeg wrote no output at %s", dst)
+	}
+	return nil
+}