feat(FN-3307): add pinch-to-zoom, auto-fit, mobile layout, and empty state

Merges five branches: adds pinch-to-zoom, mobile layout, auto-fit, and empty state to the dependency graph plugin with full test coverage; implements API key fallback resolution for models.json; restores Claude usage tracking with Fusion Anthropic auth storage; and boosts dashboard test performance

Fusion-Task-Id: FN-3307

plugins/fusion-plugin-dependency-graph/README.md

@@ -9,3 +9,27 @@ Plugin-provided top-level **Graph** dashboard view for Fusion.
   - `kb:${projectId}:dependency-graph-positions`
 
 The first version uses a lightweight custom SVG/HTML renderer (no React Flow dependency).
+
+## Mobile Support
+
+The dependency graph view is fully usable on mobile devices:
+
+- **Pinch-to-zoom** — Two-finger pinch gestures scale the graph proportionally, clamped to `[0.4×, 2×]`
+- **Mouse wheel zoom** — Desktop users can scroll-wheel to zoom toward the pointer position
+- **Auto-fit on mobile** — On initial mobile load, the graph automatically fits all nodes into the viewport
+- **Touch-friendly controls** — Zoom In, Zoom Out, and Fit buttons have 44px minimum touch targets on mobile
+- **Sticky control bar** — Controls remain accessible at the top of the viewport while panning the graph on mobile
+- **Touch-action isolation** — `touch-action: none` on the canvas prevents browser gesture interference with custom pan/zoom
+- **Empty state** — When no active tasks exist, a centered message guides the user instead of showing an empty canvas
+
+### Supported Interactions
+
+| Input | Action |
+|-------|--------|
+| Single pointer drag on canvas | Pan the graph |
+| Single pointer drag on node | Move the node |
+| Single pointer click on node | Open task detail |
+| Two-finger pinch | Zoom in/out |
+| Mouse wheel | Zoom toward pointer |
+| Zoom In / Zoom Out buttons | Step zoom ±0.1× |
+| Fit button | Auto-fit all nodes to viewport |