Add task priority enum and rename priority to rank

The existing integer priority field represents positional ordering
within a state, not semantic importance. Rename it to rank and
introduce a new priority field with enum values URGENT, HIGH,
MEDIUM and LOW across the entire stack.

Rank is now scoped to (state, priority) so tasks are ordered
within each priority group. A generated priority_rank column
combines both fields into a single sortable integer for cursor
pagination.

Dragging a task across priority groups updates its priority
automatically based on the drop position neighbors. The backend
first moves the task to the new group then repositions it at the
target rank.

The migration defaults existing rows to MEDIUM priority and
backfills ranks per (state, priority) group.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/server/api/mcp/v1/schema.resolvers.go

@@ -1896,6 +1896,7 @@ func (r *Resolver) UpdateTaskTool(ctx context.Context, req *mcp.CallToolRequest,
 			Description:  UnwrapOmittable(input.Description),
 			State:        input.State,
 			Priority:     input.Priority,
+			Rank:         input.Rank,
 			TimeEstimate: UnwrapOmittable(input.TimeEstimate),
 			Deadline:     UnwrapOmittable(input.Deadline),
 			AssignedToID: UnwrapOmittable(input.AssignedToID),

pkg/server/api/mcp/v1/specification.yaml

@@ -4621,7 +4621,7 @@ components:
     TaskOrderField:
       type: string
       enum:
-        - PRIORITY
+        - PRIORITY_RANK
         - CREATED_AT
       go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.TaskOrderField
 
@@ -4638,6 +4638,15 @@ components:
           $ref: "#/components/schemas/OrderDirection"
           description: Task order direction
 
+    TaskPriority:
+      type: string
+      enum:
+        - URGENT
+        - HIGH
+        - MEDIUM
+        - LOW
+      go.probo.inc/mcpgen/type: go.probo.inc/probo/pkg/coredata.TaskPriority
+
     Task:
       type: object
       required:
@@ -4646,6 +4655,7 @@ components:
         - name
         - state
         - priority
+        - rank
         - created_at
         - updated_at
       properties:
@@ -4676,8 +4686,11 @@ components:
           $ref: "#/components/schemas/TaskState"
           description: Task state
         priority:
+          $ref: "#/components/schemas/TaskPriority"
+          description: Task priority level
+        rank:
           type: integer
-          description: Task priority within state
+          description: Task rank within state
         time_estimate:
           anyOf:
             - $ref: "#/components/schemas/Duration"
@@ -4830,8 +4843,15 @@ components:
               description: No state
           description: Task state
         priority:
+          anyOf:
+            - $ref: "#/components/schemas/TaskPriority"
+              description: Task priority level
+            - type: "null"
+              description: No priority
+          description: Task priority level
+        rank:
           type: integer
-          description: Task priority within state
+          description: Task rank within state
         time_estimate:
           anyOf:
             - $ref: "#/components/schemas/Duration"

pkg/server/api/mcp/v1/types/task.go

@@ -26,6 +26,7 @@ func NewTask(t *coredata.Task) *Task {
 		Description:  t.Description,
 		State:        t.State,
 		Priority:     t.Priority,
+		Rank:         t.Rank,
 		TimeEstimate: t.TimeEstimate,
 		CreatedAt:    t.CreatedAt,
 		UpdatedAt:    t.UpdatedAt,