fix: search zoom coordinates, rewrite matrix as directory-level drill-down

Search fix:
- Use sigma.getNodeDisplayData() + viewportToGraph() for camera zoom
  instead of raw graph attributes. The ForceAtlas2 coordinates don't
  map directly to sigma's camera space.
- Also fixed double-click zoom using same approach
- 100ms delay before camera animate so reducer applies first

Matrix rewrite:
- Default view now shows directory-to-directory relationships (~15 dirs)
  instead of 239 files. Actually readable and useful.
- Each cell shows the number of imports between directories
- Click a directory row to drill into file-level within that directory
- Back button to return to directory overview
- Cell sizes scale with matrix size for readability
- Numbers visible in cells for non-zero values
- Hover tooltip shows full paths and import count
- Circular dependency detection at both directory and file level

Author: DevanshuNEU

frontend/src/components/DependencyGraph/GraphView/SearchBar.tsx

@@ -49,15 +49,19 @@ export function SearchBar({ onFocusNode }: SearchBarProps) {
     // pin this node (parent handles highlight via reducers)
     onFocusNode(nodeId)
 
-    // zoom camera to node using graph coordinates
-    const attrs = graph.getNodeAttributes(nodeId)
-    // small delay so the reducer applies before camera moves
+    // zoom: get the node's position in sigma's coordinate system
+    // nodeDisplayData gives us the rendered position which we can use directly
     setTimeout(() => {
-      sigma.getCamera().animate(
-        { x: attrs.x as number, y: attrs.y as number, ratio: 0.2 },
-        { duration: 500 }
-      )
-    }, 50)
+      const displayData = sigma.getNodeDisplayData(nodeId)
+      if (displayData) {
+        // convert viewport pixel coords to graph coords for the camera
+        const graphCoords = sigma.viewportToGraph({ x: displayData.x, y: displayData.y })
+        sigma.getCamera().animate(
+          { x: graphCoords.x, y: graphCoords.y, ratio: 0.2 },
+          { duration: 500 }
+        )
+      }
+    }, 100)
 
     setQuery('')
     setResults([])

frontend/src/components/DependencyGraph/GraphView/index.tsx

@@ -107,13 +107,14 @@ function Interactions({
         onSelectFile?.(node)
       },
       doubleClickNode: ({ node }) => {
-        const graph = sigma.getGraph()
-        if (!graph.hasNode(node)) return
-        const attrs = graph.getNodeAttributes(node)
-        sigma.getCamera().animate(
-          { x: attrs.x as number, y: attrs.y as number, ratio: 0.12 },
-          { duration: 400 }
-        )
+        const displayData = sigma.getNodeDisplayData(node)
+        if (displayData) {
+          const graphCoords = sigma.viewportToGraph({ x: displayData.x, y: displayData.y })
+          sigma.getCamera().animate(
+            { x: graphCoords.x, y: graphCoords.y, ratio: 0.12 },
+            { duration: 400 }
+          )
+        }
       },
       clickStage: () => {
         // clear pinned state when clicking empty space