feat(commands): add task command

Author: apiad

.opencode/commands/task.md

@@ -0,0 +1,15 @@
+---
+description: Manage tasks in tasks.yaml - add, start, cancel, archive, list, attach-plan
+agent: query
+---
+
+Task management commands using the `task` tool.
+
+### Actions
+
+- **list**: `task list` - Show all tasks (default if no action specified)
+- **add**: `task add --label "X" --description "Y" --category "Z"`
+- **start**: `task start --task-id X.X`
+- **cancel**: `task cancel --task-id X.X`
+- **archive**: `task archive --task-id X.X`
+- **attach-plan**: `task attach-plan --task-id X.X --plan-path plans/my-plan.md`