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/canvas/TileMap.js

@@ -30,8 +30,8 @@ export class TileMap {
         const x = c * ts + offsetX;
         const y = r * ts + offsetY;
 
-        // 화면 밖이면 스킵
-        if (x + ts < 0 || y + ts < 0 || x > ctx.canvas.width || y > ctx.canvas.height) continue;
+        // 화면 밖이면 스킵 (CSS 공간 기준 — DPR 변환 적용된 좌표계)
+        if (x + ts < 0 || y + ts < 0 || x > ctx.canvas.clientWidth || y > ctx.canvas.clientHeight) continue;
 
         if (tileType === 0) {
           // 벽