feat(#69): IMP-40 u1~u6 frame contract label_default placeholder/fallback role discriminator (BIM/DX leak fix)

- catalog (frame_contracts.yaml): F18 bim_dx_comparison_table col_a/col_b
  label_default_role=placeholder; F30 industry_current_status_three_col +
  F31 industry_characteristics_three_col col_a/col_b/col_c forward-compat
  placeholder; F33 engn_sw_three_types untouched (no label_default).
- mapper (_build_compare_table_2col): generic _resolve_label_default(col_key)
  branches on <col>_label_default_role — placeholder -> '' (Figma placeholder
  suppressed at runtime), fallback -> catalog literal (legacy default), unknown
  -> ValueError with template_id + role_key + value. Absent role defaults to
  fallback (backward compat for contracts without discriminator).
- tests (tests/phase_z2/test_imp40_label_default_role.py): u4 generic matrix
  (placeholder / fallback / absent / unknown / 3-col axis) + u5 F18-reuse
  non-BIM/DX synthetic rows asserting placeholder labels emit '' and BIM/DX
  literal tokens do not leak.
- snapshot (tests/integration/__snapshots__/slot_payload.json): mdx 01 F18
  string_slot_nonempty.col_a_label/col_b_label True -> False (u6 expected
  drift from u3 placeholder -> empty string flip). slot_names + rows + title
  preserved.

Verification:
- imp40_label_default_role: 6/6 PASSED
- phase_z2 sweep: 608/608 PASSED
- multi_mdx_regression: 50/50 PASSED
- cross-suite sweep: 662/662 PASSED
- BIM/DX literal grep on mapper + new test: 0 hits
- No mdx-specific branches (mdx 03/04/05 grep on mapper: 0 hits)

Guardrails: no MDX 03/04/05 hardcoding (catalog policy only); no spacing
shrink; no auto frame swap on reject; no AI call at Step 12; F33 untouched.

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

templates/phase_z2/catalog/frame_contracts.yaml

@@ -474,7 +474,9 @@ bim_dx_comparison_table:
     builder_options:
       item_parser: compare_row_2col_item    # NEW parser — top_bullet → {label, col_a, col_b}
       col_a_label_default: "BIM"            # F1-a (Codex round 43) — explicit default
+      col_a_label_default_role: placeholder # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       col_b_label_default: "DX"             # F1-a — explicit default
+      col_b_label_default_role: placeholder # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       strip_col_prefix_aliases:             # F1-b (Codex round 43) — narrow alias 만 strip
         - "BIM"
         - "DX"
@@ -1785,8 +1787,11 @@ industry_current_status_three_col:
     builder_options:
       item_parser: compare_row_3col_item       # NEW parser placeholder — top_bullet → {label, col_a, col_b, col_c}. Peer parity with compare_row_2col_item.
       col_a_label_default: "제조업"             # F30 source column 1 label (analysis.md three_industries anchor set).
+      col_a_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       col_b_label_default: "건축"               # F30 source column 2 label.
+      col_b_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       col_c_label_default: "토목"               # F30 source column 3 label (강조 테두리 빨간색 cue — visual styling).
+      col_c_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       max_rows: 12                              # typical 4-6, overflow 보호 (peer parity with compare_table_2col max_rows 12).
 
 
@@ -1847,6 +1852,9 @@ industry_characteristics_three_col:
     builder_options:
       item_parser: compare_row_3col_item       # Shared parser with industry_current_status_three_col (F30) — top_bullet → {label, col_a, col_b, col_c}. Peer parity with compare_row_2col_item.
       col_a_label_default: "제조업"             # F31 source column 1 label (analysis.md three_industries anchor set; shared with F30).
+      col_a_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       col_b_label_default: "건축"               # F31 source column 2 label (shared with F30).
+      col_b_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       col_c_label_default: "토목"               # F31 source column 3 label (강조 테두리 빨간색 cue — visual styling; shared with F30).
+      col_c_label_default_role: placeholder    # IMP-40 (#69) — Figma visual placeholder; suppressed at runtime, NOT a fallback
       max_rows: 12                              # typical 3-4 (F31 compressed view), overflow 보호 (peer parity with compare_table_2col + F30 compare_table_3col max_rows 12).