feat: store trigger in checkpoint data, editable inputs/outputs in TUI

Write the actual triggering event type into checkpoint JSON at write
time instead of inferring from the event record. Adds editable input
fields and task output overrides to the TUI for what-if exploration.
Unique fork branch names prevent collisions on repeated forks.

docs/en/concepts/checkpointing.mdx

@@ -282,6 +282,15 @@ crewai checkpoint --location ./.checkpoints.db
 
 The left panel is a tree view. Checkpoints are grouped by branch, and forks nest under the checkpoint they diverged from. Select a checkpoint to see its metadata, entity state, and task progress in the detail panel. Hit **Resume** to pick up where it left off, or **Fork** to start a new branch from that point.
 
+### Editing inputs and task outputs
+
+When a checkpoint is selected, the detail panel shows:
+
+- **Inputs** — if the original kickoff had inputs (e.g. `{topic}`), they appear as editable fields pre-filled with the original values. Change them before resuming or forking.
+- **Task outputs** — completed tasks show their output in editable text areas. Edit a task's output to change the context that downstream tasks receive. When you modify a task output and hit Fork, all subsequent tasks are invalidated and re-run with the new context.
+
+This is useful for "what if" exploration — fork from a checkpoint, tweak a task's result, and see how it changes downstream behavior.
+
 ### Subcommands
 
 ```bash