fix(navigation): block desk_cubicle in nav grid with zero padding to prevent walk-through (#75)

- desk_cubicle now has blocksNavigation: true with navPadding: 0
  (tight blocking, no inflation — aisles stay clear)
- buildNavGrid reads per-item navPadding from ITEM_METADATA
- getDeskLocations targets y-5 (chair position, above desk blocked zone)
- Agents route AROUND desks instead of through them
- Chair stays passable so agents can reach their sitting position

Fixes object passthrough for desks. Other large passable items
(doors, lamps) unchanged — they remain non-blocking by design.

Co-authored-by: Neo (subagent) <neo@openclaw.local>
Co-authored-by: Luke The Dev <252071647+iamlukethedev@users.noreply.github.com>

tests/unit/navigation.navBlockers.test.ts

@@ -203,17 +203,19 @@ describe("buildNavGrid + astar – full pathfinding integration (issue #4)", ()
 });
 
 describe("buildNavGrid – specific non-blocking item types (issue #4)", () => {
-  it("desk_cubicle does NOT block navigation — agents stand at these", () => {
+  it("desk_cubicle blocks navigation with zero padding — agents route around desks", () => {
     /*
-     * desk_cubicle has blocksNavigation: false in ITEM_METADATA.
-     * Agents interact with desks by standing beside them; the desk itself
-     * is not a solid blocker in the pathfinding grid.
+     * desk_cubicle has blocksNavigation: true with navPadding: 0 in ITEM_METADATA.
+     * The desk body is blocked in the nav grid so agents route around it,
+     * but zero padding keeps aisles between desks navigable.
+     * Agents sit at the chair position (y - 5), which is above the blocked zone.
      */
     const item = makeItem("desk_cubicle", 400, 300);
     const grid = buildNavGrid([item]);
-    expect(isBlocked(grid, 400, 300)).toBe(false);
+    expect(isBlocked(grid, 400, 300)).toBe(true);
     // Confirm via metadata as the authoritative source.
-    expect(ITEM_METADATA["desk_cubicle"]?.blocksNavigation).toBe(false);
+    expect(ITEM_METADATA["desk_cubicle"]?.blocksNavigation).toBe(true);
+    expect(ITEM_METADATA["desk_cubicle"]?.navPadding).toBe(0);
   });
 
   it("door does NOT block navigation — agents must be able to walk through doors", () => {