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/api/deploys.go

@@ -1,7 +1,7 @@
 package api
 
 import (
-	"log"
+	"log/slog"
 	"net/http"
 	"strconv"
 	"strings"
@@ -61,7 +61,7 @@ func (s *Server) inspectImage(w http.ResponseWriter, r *http.Request) {
 	// Split image:tag for the pull call.
 	imageRef, tag := splitImageTag(req.Image)
 	if err := s.docker.PullImage(ctx, imageRef, tag, ""); err != nil {
-		log.Printf("[api] pull image %s for inspect: %v", req.Image, err)
+		slog.Warn("pull image for inspect", "image", req.Image, "error", err)
 		// Try to inspect anyway in case the image is already local.
 	}