feat: add bidirectional comment system and agent input request flow

- Add Comment model and CRUD operations (repository, service layers)
- Add WAITING_FOR_INPUT task state for agent input requests
- Add WebSocket actions for comment.add, comment.get, comment.list
- Add ActionCommentAdded and ActionInputRequested notifications
- Update PromptAgent to return PromptResult with stop reason
- Add e2e test for agent input request flow
- Add PR template for the repository

This enables agents to request input from users by returning
stopReason 'needs_input' which transitions the task to
WAITING_FOR_INPUT state and creates an agent comment.

apps/backend/pkg/api/v1/task.go

@@ -6,13 +6,14 @@ import "time"
 type TaskState string
 
 const (
-	TaskStateTODO       TaskState = "TODO"
-	TaskStateInProgress TaskState = "IN_PROGRESS"
-	TaskStateReview     TaskState = "REVIEW"
-	TaskStateBlocked    TaskState = "BLOCKED"
-	TaskStateCompleted  TaskState = "COMPLETED"
-	TaskStateFailed     TaskState = "FAILED"
-	TaskStateCancelled  TaskState = "CANCELLED"
+	TaskStateTODO            TaskState = "TODO"
+	TaskStateInProgress      TaskState = "IN_PROGRESS"
+	TaskStateReview          TaskState = "REVIEW"
+	TaskStateBlocked         TaskState = "BLOCKED"
+	TaskStateWaitingForInput TaskState = "WAITING_FOR_INPUT"
+	TaskStateCompleted       TaskState = "COMPLETED"
+	TaskStateFailed          TaskState = "FAILED"
+	TaskStateCancelled       TaskState = "CANCELLED"
 )
 
 // Task represents a Kanban task
@@ -74,3 +75,22 @@ type TaskEvent struct {
 	CreatedBy *string                `json:"created_by,omitempty"`
 	CreatedAt time.Time              `json:"created_at"`
 }
+
+// Comment represents a comment on a task (user or agent)
+type Comment struct {
+	ID            string    `json:"id"`
+	TaskID        string    `json:"task_id"`
+	AuthorType    string    `json:"author_type"` // "user" or "agent"
+	AuthorID      string    `json:"author_id,omitempty"`
+	Content       string    `json:"content"`
+	RequestsInput bool      `json:"requests_input"` // True if agent is requesting user input
+	CreatedAt     time.Time `json:"created_at"`
+}
+
+// CreateCommentRequest for adding a comment to a task
+type CreateCommentRequest struct {
+	TaskID        string `json:"task_id" binding:"required"`
+	Content       string `json:"content" binding:"required"`
+	AuthorType    string `json:"author_type,omitempty"` // Defaults to "user" if not specified
+	RequestsInput bool   `json:"requests_input,omitempty"`
+}