docs(FN-3730): document missing dependency graph behaviors

- Add task detail open/clear selection interaction notes for graph cards
- Document dependency-chain highlight and dimming behavior for hover/selection
- Describe drag reposition threshold and zoom-aware pointer tracking
- Add localStorage position persistence key and fit-to-graph reset behavior

Fusion-Task-Id: FN-3730

docs/dashboard-guide.md

@@ -57,6 +57,10 @@ Behavior:
 - Supports cursor-centered wheel zoom, pinch zoom, keyboard shortcuts (`Ctrl/Cmd+=`, `Ctrl/Cmd+-`, `Ctrl/Cmd+0`, `Ctrl/Cmd+Shift+F`, `Escape`), and fit/reset controls via the floating toolbar with live zoom percentage
 - Dependency graph nodes reuse the same `TaskCard` UI as board/list views, so status badges, progress/steps, mission badges, retry/archive controls, and active-task glow stay visually consistent
 - Active graph nodes also add a dedicated top status indicator bar and current-step row highlighting so in-progress execution state stays visible even when zoomed out
+- Clicking a graph card opens task details via the host detail handler (`onOpenDetail`, with `onOpenTaskDetail` fallback), while clicking the same card again or empty canvas clears selection
+- Hovering or selecting a node highlights its full upstream and downstream dependency chain; highlighted nodes and connecting edges are emphasized while non-chain nodes are dimmed, and highlight clears when hover/selection is removed
+- Nodes support manual drag repositioning with a 4px movement threshold to separate click from drag, using pointer capture and zoom-aware delta scaling for reliable tracking
+- Custom node positions persist per project in browser localStorage (`kb:${projectId}:fusion-plugin-dependency-graph:positions`) across refresh/project switches, and **Fit to graph** clears saved positions and restores auto-layout
 
 ## Chat View