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/sse.go

@@ -4,7 +4,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
-	"log"
+	"log/slog"
 	"net/http"
 	"strings"
 
@@ -68,7 +68,7 @@ func (s *Server) streamDeployLogs(w http.ResponseWriter, r *http.Request) {
 	// Send existing logs first.
 	existingLogs, err := s.store.GetDeployLogs(deployID)
 	if err != nil {
-		log.Printf("[sse] failed to get existing deploy logs: %v", err)
+		slog.Error("get existing deploy logs", "error", err)
 	} else {
 		for _, entry := range existingLogs {
 			writeSSE(w, flusher, events.Event{
@@ -174,7 +174,7 @@ func (s *Server) streamEvents(w http.ResponseWriter, r *http.Request) {
 func writeSSE(w http.ResponseWriter, flusher http.Flusher, evt events.Event) {
 	data, err := json.Marshal(evt)
 	if err != nil {
-		log.Printf("[sse] marshal event: %v", err)
+		slog.Error("marshal SSE event", "error", err)
 		return
 	}
 	fmt.Fprintf(w, "data: %s\n\n", data)