FN-5785: add group-level pull request support for branch_groups

Add a single group-level pull request path for branch_groups in task lifecycle workflows.

- add CLI task lifecycle logic to create one pull request per branch group
- update task lifecycle tests to cover grouped pull request behavior and edge cases
- document the pull/merge dashboard behavior update
- add a changeset for @runfusion/fusion patch release

Files changed:
 .changeset/fn-5785-group-pr.md                     |   7 +
 docs/dashboard-guide.md                            |   1 +
 .../src/commands/__tests__/task-lifecycle.test.ts  | 294 ++++++++++++++++++++-
 packages/cli/src/commands/task-lifecycle.ts        | 156 ++++++++++-
 4 files changed, 443 insertions(+), 15 deletions(-)

Fusion-Task-Id: FN-5785

Fusion-Task-Lineage: 3100dedd-5b41-4cde-a56c-291410563568

docs/dashboard-guide.md

@@ -593,6 +593,7 @@ Inspect task definition, logs, review feedback, comments, documents, workflow ou
 - The **Review** tab is separate from **Comments**: Review shows actionable PR/reviewer feedback and same-task revision controls, while Comments remains the general collaboration thread.
 - **Request revision** in Review resumes work on the same task ID (no refinement task): `in-progress` tasks get steering injection, while `in-review` tasks are moved back to `in-progress` for the same branch/worktree revision pass.
 - Review supports a manual **Refresh** action in-place: PR mode pulls latest GitHub review state/decision, while direct mode rehydrates reviewer-agent feedback from persisted task data (no GitHub call).
+- For shared `branch_groups` (tasks with `branchContext.groupId`), PR merge mode opens and tracks one group-level PR from the group integration branch to the project default branch; member tasks share that PR state.
 - In direct/non-PR auto-merge mode, Review renders normalized reviewer-agent feedback (verdict/step/timestamp/detail) with dedicated loading/error/empty states; it does not require users to read raw agent logs.
 
 ### Identifying high-impact blockers