feat(#91): IMP-91 u2~u15 multi-mdx regression CI suite + status-board auto-update

- u2~u5: tests/integration/test_multi_mdx_regression.py — MDX_SET=(01..05)
  cached integration runs + status/structural/visual snapshots +
  full_mdx_coverage assertion (9 snapshots populated for 01-05).
- u6~u11: F0 normalize / F1 V4 ranking / F2 slot_payload /
  F3 classifier-only AI / F4 layout / F5 final.html axis per MDX_SET.
- u12: pyproject.toml — pytest-json-report>=1.5 in dev extras.
- u13: .github/workflows/multi-mdx-regression.yml — pytest+artifact CI.
- u14: scripts/update_status_board.py + tests/scripts/test_update_status_board.py
  — idempotent JSON marker updater (3 unit tests pass).
- u15: PHASE-Z-PIPELINE-STATUS-BOARD.md — 30 F0-F5 × mdx01-05 markers
  initialized `?` + workflow wiring.

Stage 4 verify: 59/59 PASS targeted (smoke 6 + updater 3 + integration 50),
386/386 PASS regression umbrella, 0 failures.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/integration/__snapshots__/visual.json

@@ -0,0 +1,48 @@
+{
+  "_doc": "u4 — pin observed step14_visual_check overflow/clip per mdx 01-05. Fresh subprocess observation per [[feedback_validation_first_for_closed_issues]]; drift surfaces visual regression (overflow / clip) loudly per [[feedback_artifact_status_naming]] 3-axis honesty. Snapshot pinned to current-state, not to invented expectation (Stage 1 scope-lock).",
+  "01": {
+    "slide_overflowed": false,
+    "slide_body_overflowed": false,
+    "passed": true,
+    "zones": [
+      {"position": "top", "template_id": "bim_dx_comparison_table", "overflowed": false, "clipped_inner_count": 0},
+      {"position": "bottom", "template_id": "construction_bim_three_usage", "overflowed": false, "clipped_inner_count": 0}
+    ]
+  },
+  "02": {
+    "slide_overflowed": false,
+    "slide_body_overflowed": false,
+    "passed": true,
+    "zones": [
+      {"position": "top", "template_id": "construction_goals_three_circle_intersection", "overflowed": false, "clipped_inner_count": 0},
+      {"position": "bottom", "template_id": "__empty__", "overflowed": false, "clipped_inner_count": 0}
+    ]
+  },
+  "03": {
+    "slide_overflowed": false,
+    "slide_body_overflowed": false,
+    "passed": true,
+    "zones": [
+      {"position": "left", "template_id": "three_parallel_requirements", "overflowed": false, "clipped_inner_count": 0},
+      {"position": "right", "template_id": "process_product_two_way", "overflowed": false, "clipped_inner_count": 0}
+    ]
+  },
+  "04": {
+    "slide_overflowed": false,
+    "slide_body_overflowed": false,
+    "passed": true,
+    "zones": [
+      {"position": "top", "template_id": "bim_issues_quadrant_four", "overflowed": false, "clipped_inner_count": 0},
+      {"position": "bottom-left", "template_id": "__empty__", "overflowed": false, "clipped_inner_count": 0},
+      {"position": "bottom-right", "template_id": "__empty__", "overflowed": false, "clipped_inner_count": 0}
+    ]
+  },
+  "05": {
+    "slide_overflowed": false,
+    "slide_body_overflowed": false,
+    "passed": true,
+    "zones": [
+      {"position": "primary", "template_id": "__empty__", "overflowed": false, "clipped_inner_count": 0}
+    ]
+  }
+}