feat(step14+step21): add zone_geometries_px artifact (IMP-01 #1)

- Add slide-relative bbox export of .zone elements via getBoundingClientRect
- Inline Selenium JS collects zone_geometries_px = [{position, template_id, x, y, w, h}]
- write_debug_json adds top-level additive zone_geometries_px field
- Existing visual_runtime_check / zones / frame_slot_metrics / PASS/FAIL logic unchanged
- AI/Kei/V4/frame selection paths not touched

Refs Gitea #1 (IMP-01 A-6 Zone DOM 좌표 export)

src/phase_z2_pipeline.py

@@ -850,11 +850,14 @@ def run_overflow_check(html_path: Path) -> dict:
 
             const slideM = measure(slide);
             slideM.size_correct = slide.clientWidth === 1280 && slide.clientHeight === 720;
+            // A-6 (IMP-01 #1) — slide-relative bbox base
+            const slideRect = slide.getBoundingClientRect();
 
             const body = document.querySelector('.slide-body');
             const bodyM = body ? measure(body) : null;
 
             const zones = [];
+            const zone_geometries_px = [];
             slide.querySelectorAll('.zone').forEach((z) => {
                 const pos = z.getAttribute('data-zone-position') || 'unknown';
                 const tid = z.getAttribute('data-template-id') || '?';
@@ -862,6 +865,17 @@ def run_overflow_check(html_path: Path) -> dict:
                 m.position = pos;
                 m.template_id = tid;
 
+                // A-6 (IMP-01 #1) — zone bbox in slide-relative px (additive trace, no layout side effect)
+                const zoneRect = z.getBoundingClientRect();
+                zone_geometries_px.push({
+                    position: pos,
+                    template_id: tid,
+                    x: Math.round(zoneRect.left - slideRect.left),
+                    y: Math.round(zoneRect.top - slideRect.top),
+                    w: Math.round(zoneRect.width),
+                    h: Math.round(zoneRect.height),
+                });
+
                 // 내부 clipping 검사 — frame-family root/cell 단위.
                 // tolerance / threshold 그대로. inner_content_signals 만 추가 보강 (detection 데이터 늘림).
                 const clipped = [];
@@ -926,7 +940,7 @@ def run_overflow_check(html_path: Path) -> dict:
                 });
             });
 
-            return { slide: slideM, slide_body: bodyM, zones, frame_slot_metrics };
+            return { slide: slideM, slide_body: bodyM, zones, frame_slot_metrics, zone_geometries_px };
         """)
 
         screenshot_path = html_path.parent / "preview.png"
@@ -1228,6 +1242,8 @@ def write_debug_json(run_dir: Path, layout_preset: str,
         "composition_planner_debug": composition_debug,
         "zones": debug_zones,
         "visual_runtime_check": visual_runtime_check,
+        # A-6 (IMP-01 #1) — additive top-level zone bbox trace (slide-relative px)
+        "zone_geometries_px": (visual_runtime_check or {}).get("zone_geometries_px", []),
     }
     debug_path = run_dir / "debug.json"
     debug_path.write_text(json.dumps(debug, ensure_ascii=False, indent=2), encoding="utf-8")