feat(observability+tts): OTel logs for backend/runner/ui; add kokoro-fastapi (GPU) and pocket-tts (CPU) to homelab

- otelsetup.Init now returns a *slog.Logger wired to the OTLP log exporter
  so all slog output is shipped to Loki with embedded trace IDs
- backend and runner both adopt the new OTel-bridged logger
- runner.runScrapeTask and runAudioTask now emit structured OTel spans
- ui/hooks.server.ts adds BatchLogRecordProcessor alongside existing trace exporter
- homelab: add kokoro-fastapi GPU service (ghcr.io/remsky/kokoro-fastapi-gpu)
  using deploy.resources.reservations for NVIDIA GPU, exposed internally on :8880
- homelab: add pocket-tts CPU service (ghcr.io/kyutai-labs/pocket-tts) on :8000
- runner KOKORO_URL hardcoded to http://kokoro-fastapi:8880 (fixes DNS failure
  for the stale kokoro.kalekber.cc hostname)

backend/internal/otelsetup/otelsetup.go

@@ -5,12 +5,13 @@
 //	OTEL_EXPORTER_OTLP_ENDPOINT  — OTLP/HTTP endpoint, e.g. http://otel-collector:4318
 //	OTEL_SERVICE_NAME            — service name reported in traces (default: "backend")
 //
-// When OTEL_EXPORTER_OTLP_ENDPOINT is empty the function is a no-op and
-// returns a nil shutdown func, so the caller never needs to branch on it.
+// When OTEL_EXPORTER_OTLP_ENDPOINT is empty the function is a no-op: it
+// returns a nil shutdown func and the default slog.Logger, so callers never
+// need to branch on it.
 //
 // Usage in main.go:
 //
-//	shutdown, err := otelsetup.Init(ctx, version)
+//	shutdown, log, err := otelsetup.Init(ctx, version)
 //	if err != nil { return err }
 //	if shutdown != nil { defer shutdown() }
 package otelsetup
@@ -18,22 +19,31 @@ package otelsetup
 import (
 	"context"
 	"fmt"
+	"log/slog"
 	"os"
 	"time"
 
+	"go.opentelemetry.io/contrib/bridges/otelslog"
 	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploghttp"
 	"go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracehttp"
+	otellog "go.opentelemetry.io/otel/log/global"
+	"go.opentelemetry.io/otel/sdk/log"
 	"go.opentelemetry.io/otel/sdk/resource"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 	semconv "go.opentelemetry.io/otel/semconv/v1.26.0"
 )
 
-// Init sets up a TracerProvider that exports spans via OTLP/HTTP.
-// Returns a shutdown function (or nil if OTel is disabled) and any error.
-func Init(ctx context.Context, version string) (shutdown func(), err error) {
+// Init sets up TracerProvider and LoggerProvider that export via OTLP/HTTP.
+//
+// Returns:
+//   - shutdown: flushes and stops both providers (nil when OTel is disabled).
+//   - logger:   an slog.Logger bridged to OTel logs (falls back to default when disabled).
+//   - err:      non-nil only on SDK initialisation failure.
+func Init(ctx context.Context, version string) (shutdown func(), logger *slog.Logger, err error) {
 	endpoint := os.Getenv("OTEL_EXPORTER_OTLP_ENDPOINT")
 	if endpoint == "" {
-		return nil, nil // OTel disabled — not an error
+		return nil, slog.Default(), nil // OTel disabled — not an error
 	}
 
 	serviceName := os.Getenv("OTEL_SERVICE_NAME")
@@ -41,14 +51,7 @@ func Init(ctx context.Context, version string) (shutdown func(), err error) {
 		serviceName = "backend"
 	}
 
-	exp, err := otlptracehttp.New(ctx,
-		otlptracehttp.WithEndpoint(endpoint),
-		otlptracehttp.WithInsecure(), // collector is on the internal Docker network
-	)
-	if err != nil {
-		return nil, fmt.Errorf("otelsetup: create OTLP exporter: %w", err)
-	}
-
+	// ── Shared resource ───────────────────────────────────────────────────────
 	res, err := resource.New(ctx,
 		resource.WithAttributes(
 			semconv.ServiceName(serviceName),
@@ -56,19 +59,50 @@ func Init(ctx context.Context, version string) (shutdown func(), err error) {
 		),
 	)
 	if err != nil {
-		return nil, fmt.Errorf("otelsetup: create resource: %w", err)
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create resource: %w", err)
+	}
+
+	// ── Trace provider ────────────────────────────────────────────────────────
+	traceExp, err := otlptracehttp.New(ctx,
+		otlptracehttp.WithEndpoint(endpoint),
+		otlptracehttp.WithInsecure(), // collector is on the internal Docker network
+	)
+	if err != nil {
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create OTLP trace exporter: %w", err)
 	}
 
 	tp := sdktrace.NewTracerProvider(
-		sdktrace.WithBatcher(exp),
+		sdktrace.WithBatcher(traceExp),
 		sdktrace.WithResource(res),
 		sdktrace.WithSampler(sdktrace.ParentBased(sdktrace.TraceIDRatioBased(0.2))),
 	)
 	otel.SetTracerProvider(tp)
 
-	return func() {
+	// ── Log provider ──────────────────────────────────────────────────────────
+	logExp, err := otlploghttp.New(ctx,
+		otlploghttp.WithEndpoint(endpoint),
+		otlploghttp.WithInsecure(),
+	)
+	if err != nil {
+		return nil, slog.Default(), fmt.Errorf("otelsetup: create OTLP log exporter: %w", err)
+	}
+
+	lp := log.NewLoggerProvider(
+		log.WithProcessor(log.NewBatchProcessor(logExp)),
+		log.WithResource(res),
+	)
+	otellog.SetLoggerProvider(lp)
+
+	// Bridge slog → OTel logs. Structured fields and trace IDs are forwarded
+	// automatically; Grafana can correlate log lines with Tempo traces.
+	otelLogger := otelslog.NewLogger(serviceName)
+
+	shutdown = func() {
 		shutCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
 		_ = tp.Shutdown(shutCtx)
-	}, nil
+		_ = lp.Shutdown(shutCtx)
+	}
+
+	return shutdown, otelLogger, nil
 }