feat(labels): standardize automatic label creation to match ecosystem convention

@goal: WHOOSH-LABELS-004, WSH-CONSISTENCY - Ecosystem standardization

Replace custom label set with standardized CHORUS ecosystem labels:
- Add all 8 GitHub-standard labels (bug, duplicate, enhancement, etc.)
- Fix bzzz-task color from #ff6b6b to #5319e7 for consistency
- Remove custom priority labels and whoosh-monitored label
- Maintain backward compatibility and error handling

Changes:
- Updated EnsureRequiredLabels() in internal/gitea/client.go
- Added requirement traceability comments throughout
- Updated integration points in internal/server/server.go
- Created comprehensive decision record

Benefits:
- Consistent labeling across WHOOSH, CHORUS, KACHING repositories
- Familiar GitHub-standard labels for better developer experience
- Improved tool integration and issue management
- Preserved bzzz-task automation for CHORUS workflow

Fixes: WHOOSH issue #4

🤖 Generated with [Claude Code](https://claude.ai/code)

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

internal/server/server.go

@@ -2352,11 +2352,14 @@ func (s *Server) createRepositoryHandler(w http.ResponseWriter, r *http.Request)
 	}
 	
 	// Automatically create required labels in the Gitea repository
+	// @goal: WHOOSH-LABELS-004 - Automatic label creation on repository addition
+	// WHY: Ensures standardized ecosystem labels are available immediately for issue categorization
 	if req.SourceType == "gitea" && s.repoMonitor != nil && s.repoMonitor.GetGiteaClient() != nil {
 		log.Info().
 			Str("repository", fullName).
 			Msg("Creating required labels in Gitea repository")
-		
+
+		// @goal: WHOOSH-LABELS-004 - Apply standardized label set to new repository
 		err := s.repoMonitor.GetGiteaClient().EnsureRequiredLabels(context.Background(), req.Owner, req.Name)
 		if err != nil {
 			log.Warn().
@@ -2634,7 +2637,8 @@ func (s *Server) ensureRepositoryLabelsHandler(w http.ResponseWriter, r *http.Re
 		return
 	}
 	
-	// Ensure required labels exist
+	// @goal: WHOOSH-LABELS-004 - Manual label synchronization endpoint
+	// WHY: Allows updating existing repositories to standardized label set
 	err = s.repoMonitor.GetGiteaClient().EnsureRequiredLabels(context.Background(), owner, name)
 	if err != nil {
 		log.Error().