feat(FN-4161): preserve github tracking detail after restart

Fixed GitHub issue tracking details (URL, repo, issue number) being lost when an executor restarts mid-task, with tests and docs to guard against regression.

Fusion-Task-Id: FN-4161

docs/task-management.md

@@ -428,6 +428,7 @@ Tracking behavior is controlled per task:
 - `task.githubTracking.enabled` turns tracking on for that task.
 - `task.githubTracking.repoOverride` optionally forces a specific target repo (`owner/repo`).
 - In the dashboard **Task Detail** modal, eligible existing tasks (`triage`, `todo`, `in-progress`, `in-review`) always show a compact GitHub tracking summary row. When tracking is currently disabled and editable, the header exposes a one-click **Enable GitHub tracking** button; linked-issue details and the rest of the tracking controls remain behind the disclosure arrow for disable/retarget flows.
+- After an engine/dashboard restart, Task Detail preserves the fetched full `githubTracking` payload even when the board opened the modal from a slim task row that intentionally omitted tracking metadata.
 - When a task is already tracking-enabled but still unlinked, Task Detail exposes a **Create tracking issue** action in the disclosure content (including non-editable columns like `done`) so "Issue not yet created" is not a dead-end state.
 - Clearing the Task Detail repo override stores `null`, which reverts repo resolution to project/global defaults.
 - Explicit task-level enablement is honored even when project/global GitHub tracking defaults are unset. If `enabled: true` and the repo resolves at task scope (for example via `repoOverride`), Fusion attempts tracking-issue creation on both create-time and eligible edit-time flows.