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/transcribe/chain.go

@@ -0,0 +1,53 @@
+package transcribe
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	"git.d-ma.be/mathias/tapir/internal/domain"
+)
+
+// Backend is one transcription endpoint. *Gateway satisfies it; Name is the value
+// recorded as the serving endpoint.
+type Backend interface {
+	Name() string
+	Transcribe(ctx context.Context, wavPath string) (domain.Transcription, error)
+}
+
+// Chain tries a primary (local) backend and, if it fails for ANY reason, a
+// fallback. The fallback exists because iguana can wedge permanently on a Metal
+// OOM (infra#273) — which is also why a fallback is a data-egress decision: the
+// berget endpoint is a cloud service, so the result records which one served it.
+type Chain struct {
+	primary  Backend
+	fallback Backend // nil disables the fallback
+}
+
+// NewChain builds a Chain. A nil fallback means a primary failure is the result.
+func NewChain(primary, fallback Backend) *Chain {
+	return &Chain{primary: primary, fallback: fallback}
+}
+
+// Transcribe returns the first backend's success. It falls back on any primary
+// error — transport, timeout, non-2xx, empty transcript — and never inspects a
+// response body to decide. A cancelled context stops the chain: a job the user or
+// shutdown cancelled must not ship its audio to a cloud endpoint as a last act.
+func (c *Chain) Transcribe(ctx context.Context, wavPath string) (domain.Transcription, error) {
+	t, err := c.primary.Transcribe(ctx, wavPath)
+	if err == nil {
+		t.Endpoint = c.primary.Name()
+		return t, nil
+	}
+	if c.fallback == nil || ctx.Err() != nil {
+		return domain.Transcription{}, fmt.Errorf("%s: %w", c.primary.Name(), err)
+	}
+	t, ferr := c.fallback.Transcribe(ctx, wavPath)
+	if ferr != nil {
+		return domain.Transcription{}, errors.Join(
+			fmt.Errorf("%s: %w", c.primary.Name(), err),
+			fmt.Errorf("%s: %w", c.fallback.Name(), ferr))
+	}
+	t.Endpoint = c.fallback.Name()
+	return t, nil
+}