Structured logging + request ID middleware — ingest v2.0, history v2.0, api v2.0

Migrate all log.Printf/log.Fatalf to log/slog with structured key-value
attributes per bible go-logging contract.

- Add withRequestID middleware: generates crypto/rand 8-byte hex ID per
  request, sets X-Request-ID response header, injects into context
- withErrorLogging uses slog with request_id from context
- writeError internal log calls migrated to slog.Error/slog.Warn
- All handler log calls in api, ingest, history packages use slog
- cmd/reanimator-api configures slog.NewTextHandler(os.Stdout) at startup
- cmd/reanimator-migrate, cmd/reanimator-reset migrated to slog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/reanimator-api/main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"context"
 	"errors"
-	"log"
+	"log/slog"
 	"net/http"
 	"os"
 	"os/signal"
@@ -17,34 +17,39 @@ import (
 )
 
 func main() {
-	log.SetOutput(os.Stdout)
-	log.SetFlags(log.LstdFlags | log.Lmicroseconds | log.Lshortfile)
+	slog.SetDefault(slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	})))
 
 	cfg, err := config.Load()
 	if err != nil {
-		log.Fatalf("load config: %v", err)
+		slog.Error("load config failed", "err", err)
+		os.Exit(1)
 	}
 
 	db, err := repository.Open(cfg.DatabaseDSN)
 	if err != nil {
-		log.Fatalf("open database: %v", err)
+		slog.Error("open database failed", "err", err)
+		os.Exit(1)
 	}
 	defer func() {
 		_ = db.Close()
 	}()
 	if err := migrate.EnsureSchema(db, cfg.MigrationsDir); err != nil {
-		log.Fatalf("apply migrations: %v", err)
+		slog.Error("apply migrations failed", "err", err)
+		os.Exit(1)
 	}
 	if err := migrate.ValidateOwnershipSchema(db); err != nil {
-		log.Fatalf("schema validation failed: %v", err)
+		slog.Error("schema validation failed", "err", err)
+		os.Exit(1)
 	}
-	log.Printf("database schema ready")
+	slog.Info("database schema ready")
 
 	srv := api.NewServer(cfg.HTTPAddr, cfg.ReadTimeout, cfg.WriteTimeout, db)
 
 	errCh := make(chan error, 1)
 	go func() {
-		log.Printf("starting API server on %s", cfg.HTTPAddr)
+		slog.Info("starting API server", "addr", cfg.HTTPAddr)
 		errCh <- srv.Start()
 	}()
 
@@ -53,19 +58,21 @@ func main() {
 
 	select {
 	case sig := <-signalCh:
-		log.Printf("received signal %s, shutting down", sig)
+		slog.Info("received signal, shutting down", "signal", sig)
 	case err := <-errCh:
 		if err == nil || errors.Is(err, http.ErrServerClosed) {
 			return
 		}
-		log.Fatalf("server error: %v", err)
+		slog.Error("server error", "err", err)
+		os.Exit(1)
 	}
 
 	ctx, cancel := context.WithTimeout(context.Background(), cfg.ShutdownGrace)
 	defer cancel()
 
 	if err := srv.Shutdown(ctx); err != nil {
-		log.Fatalf("shutdown server: %v", err)
+		slog.Error("shutdown server failed", "err", err)
+		os.Exit(1)
 	}
 
 	// Ensure in-flight logs flush before exit in short-lived environments.