feat(#39): IMP-30 first-render invariant + abort bypass (2 paths)

Restore first-render invariant: final.html + Step 20 slide_status MUST be
written for every input where Step 0~5 succeed. Two abort paths replaced
with provisional/empty-shell synthesis; MDX content preserved, AI-free.

- u1 V4Match.provisional + lookup_v4_match_with_fallback(allow_provisional)
  chain_exhausted -> synthesize rank-1 provisional (opt-in, default-off)
- u2 CompositionUnit.provisional propagation (single / parent_merged /
  parent_merged_inferred constructors)
- u3 select_composition_units(allow_provisional_fill=True) last-resort
  fill + _candidate_state="selected_provisional"
- u4 pipeline.py path-(a) abort guard replaced with provisional retry +
  terminal __empty__ shell (no sys.exit(1))
- u5 zones_data.provisional -> slide_base.html zone--provisional class +
  data-provisional + needs-adaptation badge (template-only)
- u6 compute_slide_status additive provisional_first_render_count/_units
  (overall enum unchanged per IMP-05 Codex #10 D4)
- u7 regression: tests/test_phase_z2_imp30_first_render.py (28 tests) +
  tests/test_phase_z2_v4_fallback.py (+5 cases)

Guardrails verified: MVP1_ALLOWED_STATUSES unchanged, no calculate_fit,
no LLM in fallback path, no MDX 03/04/05 hardcoding.

Anchor sync (Rule 13): tests/orchestrator_unit/test_imp17_comment_anchor.py
re-pinned 564/565 -> 570/571 to track V4Match.provisional shift at
src/phase_z2_pipeline.py:179-184.

Cross-ref: IMP-05 (#5) §5 defer + Codex #2 first-render invariant.

templates/phase_z2/slide_base.html

@@ -114,6 +114,43 @@
       min-height: 0;
     }
 
+    /* ── IMP-30 u5 : provisional zone marker (first-render invariant) ──
+         When V4 rank-1 candidate falls outside MVP1_ALLOWED_STATUSES (chain_exhausted)
+         the pipeline still renders the rank-1 frame so the first-render invariant
+         holds, but the zone is tagged `provisional` so the user/AI can adapt later
+         (IMP-31). Visual contract:
+           - dashed amber border + striped wash → "needs adaptation" at a glance
+           - inline badge top-right → text label for non-color-perceiving readers
+         MDX content is preserved as-is; no shrink, no rewrite. */
+    .zone--provisional {
+      outline: 2px dashed #b8860b;
+      outline-offset: -2px;
+      background-image: repeating-linear-gradient(
+        45deg,
+        rgba(184, 134, 11, 0.04) 0,
+        rgba(184, 134, 11, 0.04) 8px,
+        transparent 8px,
+        transparent 16px
+      );
+    }
+    .zone--provisional .zone__needs-adaptation-badge {
+      position: absolute;
+      top: 4px;
+      right: 4px;
+      z-index: 10;
+      padding: 2px 6px;
+      background: #b8860b;
+      color: #fff;
+      font-size: 9px;
+      font-weight: 700;
+      line-height: 1.2;
+      letter-spacing: 0.04em;
+      border-radius: 2px;
+      text-transform: uppercase;
+      pointer-events: none;
+      box-shadow: 0 1px 2px rgba(0, 0, 0, 0.15);
+    }
+
     /* ── Frame-family text layout contract (shared, reusable) ──
          feedback-1 (mvp1.5b_test7): visible improvement 강화.
          Stronger hanging indent + breathing line spacing + visible hierarchy. */
@@ -264,7 +301,8 @@
     <div class="slide-body">
       <div class="layout-{{ layout_preset }}">
         {% for zone in zones %}
-        <div class="zone" data-zone-position="{{ zone.position }}" data-template-id="{{ zone.template_id }}" style="grid-area: {{ zone.position }};">
+        <div class="zone{% if zone.provisional %} zone--provisional{% endif %}" data-zone-position="{{ zone.position }}" data-template-id="{{ zone.template_id }}"{% if zone.provisional %} data-provisional="1"{% endif %} style="grid-area: {{ zone.position }};">
+          {% if zone.provisional %}<span class="zone__needs-adaptation-badge" aria-label="needs user or AI adaptation">needs adaptation</span>{% endif %}
           {{ zone.partial_html | safe }}
         </div>
         {% endfor %}