fix(agent-office): critical bug fixes from code review — wall pathfinding, drag/click, DPR, culling

- Pathfinder.setBlocked: remove blocked.clear() to preserve wall tiles set by setWalls()
- Pathfinder.findPath: fix dead-code goal exception — remove redundant isBlocked check, keep goal-tile exception in single guard
- OfficeRenderer: track mouseDownPos/_wasDragging; expose wasDragging() method for click-after-drag suppression
- OfficeRenderer._render: track _lastDpr to detect monitor DPR changes; use setTransform instead of scale to avoid accumulation
- TileMap.render: use clientWidth/clientHeight for viewport culling (CSS space, not buffer pixels)
- TaskTab: wrap JSON.parse in try/catch to prevent crash on malformed result_data

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/agent-office/hooks/useOfficeCanvas.js

@@ -47,6 +47,10 @@ export function useOfficeCanvas() {
     return rendererRef.current?.zoom || 2;
   }, []);
 
+  const wasDragging = useCallback(() => {
+    return rendererRef.current?.wasDragging?.() || false;
+  }, []);
+
   return {
     canvasRef,
     updateAgentState,
@@ -54,6 +58,7 @@ export function useOfficeCanvas() {
     setTheme,
     setZoom,
     hitTest,
-    getZoom
+    getZoom,
+    wasDragging
   };
 }