feat(docker-watcher): phase 12 - hardening

Blue-green zero-downtime deploys, promote flow validation.
Dual auth: local (bcrypt + JWT) and OAuth2/OIDC (any provider).
Auth middleware, login page, auth settings UI.
Structured logging (slog JSON), config export to YAML.
Graceful shutdown with deploy draining.
Multi-stage Dockerfile and production docker-compose.yml.
Swap phase order: Volumes & Env before UI Polish.

internal/logging/logger.go

@@ -0,0 +1,34 @@
+package logging
+
+import (
+	"io"
+	"log/slog"
+	"os"
+)
+
+// Setup initializes the global structured JSON logger.
+// It replaces the default slog handler with a JSON handler writing to stdout.
+func Setup() {
+	handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	})
+	slog.SetDefault(slog.New(handler))
+}
+
+// SetupWithWriter initializes the global structured JSON logger writing to the given writer.
+func SetupWithWriter(w io.Writer) {
+	handler := slog.NewJSONHandler(w, &slog.HandlerOptions{
+		Level: slog.LevelInfo,
+	})
+	slog.SetDefault(slog.New(handler))
+}
+
+// DeployContext returns a logger enriched with deploy-specific attributes.
+func DeployContext(project, stage, tag, instanceID string) *slog.Logger {
+	return slog.With(
+		slog.String("project", project),
+		slog.String("stage", stage),
+		slog.String("tag", tag),
+		slog.String("instance_id", instanceID),
+	)
+}