Refactor web build process and update documentation

- Removed Node.js build artifacts from .gitignore and adjusted Makefile to reflect changes in web UI build process, now using server-rendered Go templates instead of React.
- Updated README to clarify the new web UI architecture and output formats, emphasizing the removal of the Node.js build step.
- Added a command to set the number of frames per render task in manager configuration, enhancing user control over rendering settings.
- Improved Gitea workflow by removing unnecessary npm install step, streamlining the CI process.

internal/manager/runners.go

@@ -275,7 +275,8 @@ type NextJobTaskInfo struct {
 	TaskID   int64                `json:"task_id"`
 	JobID    int64                `json:"job_id"`
 	JobName  string               `json:"job_name"`
-	Frame    int                  `json:"frame"`
+	Frame    int                  `json:"frame"`     // frame start (inclusive)
+	FrameEnd int                  `json:"frame_end"` // frame end (inclusive); same as Frame for single-frame
 	TaskType string               `json:"task_type"`
 	Metadata *types.BlendMetadata `json:"metadata,omitempty"`
 }
@@ -376,6 +377,7 @@ func (s *Manager) handleNextJob(w http.ResponseWriter, r *http.Request) {
 		TaskID        int64
 		JobID         int64
 		Frame         int
+		FrameEnd      sql.NullInt64
 		TaskType      string
 		JobName       string
 		JobUserID     int64
@@ -385,7 +387,7 @@ func (s *Manager) handleNextJob(w http.ResponseWriter, r *http.Request) {
 
 	err = s.db.With(func(conn *sql.DB) error {
 		rows, err := conn.Query(
-			`SELECT t.id, t.job_id, t.frame, t.task_type, 
+			`SELECT t.id, t.job_id, t.frame, t.frame_end, t.task_type, 
 			        j.name as job_name, j.user_id, j.blend_metadata,
 			        t.condition
 			 FROM tasks t
@@ -403,7 +405,7 @@ func (s *Manager) handleNextJob(w http.ResponseWriter, r *http.Request) {
 		for rows.Next() {
 			var task taskCandidate
 			var condition sql.NullString
-			err := rows.Scan(&task.TaskID, &task.JobID, &task.Frame, &task.TaskType,
+			err := rows.Scan(&task.TaskID, &task.JobID, &task.Frame, &task.FrameEnd, &task.TaskType,
 				&task.JobName, &task.JobUserID, &task.BlendMetadata, &condition)
 			if err != nil {
 				continue
@@ -549,6 +551,11 @@ func (s *Manager) handleNextJob(w http.ResponseWriter, r *http.Request) {
 	// Update job status
 	s.updateJobStatusFromTasks(selectedTask.JobID)
 
+	// Frame end for response: use task range or single frame (NULL frame_end)
+	frameEnd := selectedTask.Frame
+	if selectedTask.FrameEnd.Valid {
+		frameEnd = int(selectedTask.FrameEnd.Int64)
+	}
 	// Build response
 	response := NextJobResponse{
 		JobToken: jobToken,
@@ -558,6 +565,7 @@ func (s *Manager) handleNextJob(w http.ResponseWriter, r *http.Request) {
 			JobID:    selectedTask.JobID,
 			JobName:  selectedTask.JobName,
 			Frame:    selectedTask.Frame,
+			FrameEnd: frameEnd,
 			TaskType: selectedTask.TaskType,
 			Metadata: metadata,
 		},
@@ -1959,6 +1967,12 @@ func (s *Manager) updateJobStatusFromTasks(jobID int64) {
 		return
 	}
 
+	// Cancellation is terminal from the user's perspective.
+	// Do not allow asynchronous task updates to revive cancelled jobs.
+	if currentStatus == string(types.JobStatusCancelled) {
+		return
+	}
+
 	// Count total tasks and completed tasks
 	var totalTasks, completedTasks int
 	err = s.db.With(func(conn *sql.DB) error {