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/components/TaskTab.jsx

@@ -45,7 +45,12 @@ export default function TaskTab({ agentId, refreshTrigger }) {
               <span className="ao-task-time">{formatTime(task.created_at)}</span>
             </div>
             {expanded === task.id && task.result_data && (
-              <pre className="ao-task-result">{JSON.stringify(JSON.parse(task.result_data), null, 2)}</pre>
+              <pre className="ao-task-result">
+                {(() => {
+                  try { return JSON.stringify(JSON.parse(task.result_data), null, 2); }
+                  catch { return task.result_data; }
+                })()}
+              </pre>
             )}
           </div>
         );