feat(IMP-16): U1 H3 verification utility port + U2 wiring design

U1 (runtime, u1-u10): new Phase Z-owned deterministic verification module
src/phase_z2_verification_utils.py (335 LOC, stdlib only) porting H3 utility
surface — VerificationResult, extract_text_from_html, normalize_for_comparison,
extract_keywords, strip_meta_lines, split_into_sentences, verify_text_preservation,
detect_invented_text. 10 unit tests under tests/phase_z2/test_pz2_vu_*.py (56 tests).

u11 (design-only): docs/architecture/IMP-16-U2-WIRING-DESIGN.md fixes the Step
1/2/14/21/22 reverse-path contract, redesigned frame-contract pattern
reservation (IMP-20), and IMP-07 hard-gate criteria. No runtime wiring lands
in this commit — U2 stays blocked until IMP-07 reverse path is implemented +
verified + runtime-hit.

Guardrails: no src.content_verifier import; no FORBIDDEN_KEI_MEMOS /
generate_with_retry / REQUIRED_PATTERNS / verify_structure / verify_area /
verify_all_areas usage; no AI / Kei / httpx / SSE path; AI-isolation contract
upheld (utility is deterministic).

Tests: 56 targeted PASS (0.19s), 15 regression baseline PASS (7.59s).

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

tests/phase_z2/test_pz2_vu_dataclass.py

@@ -0,0 +1,59 @@
+"""u1 — VerificationResult dataclass surface (IMP-16-U1).
+
+Locks the Phase Z verification utility module anchor and the
+VerificationResult shape so downstream units (u2~u10) can rely on it
+without importing src.content_verifier.
+"""
+from __future__ import annotations
+
+import ast
+import importlib
+
+import pytest
+
+
+def test_module_importable_without_content_verifier():
+    mod = importlib.import_module("src.phase_z2_verification_utils")
+    tree = ast.parse(open(mod.__file__, encoding="utf-8").read())
+    for node in ast.walk(tree):
+        if isinstance(node, ast.Import):
+            for alias in node.names:
+                assert "content_verifier" not in alias.name, (
+                    "Phase Z verification utility must not import "
+                    "src.content_verifier"
+                )
+        elif isinstance(node, ast.ImportFrom):
+            assert node.module is None or "content_verifier" not in node.module, (
+                "Phase Z verification utility must not import "
+                "src.content_verifier"
+            )
+
+
+def test_verification_result_defaults():
+    from src.phase_z2_verification_utils import VerificationResult
+
+    r = VerificationResult(passed=True, area_name="zone_test")
+    assert r.passed is True
+    assert r.area_name == "zone_test"
+    assert r.checks == {}
+    assert r.score == 0.0
+    assert r.errors == []
+    assert r.warnings == []
+
+
+def test_verification_result_independent_default_collections():
+    from src.phase_z2_verification_utils import VerificationResult
+
+    a = VerificationResult(passed=False, area_name="a")
+    b = VerificationResult(passed=False, area_name="b")
+    a.checks["x"] = True
+    a.errors.append("e")
+    a.warnings.append("w")
+    assert b.checks == {} and b.errors == [] and b.warnings == []
+
+
+def test_verification_result_required_fields():
+    from src.phase_z2_verification_utils import VerificationResult
+
+    with pytest.raises(TypeError):
+        VerificationResult()  # type: ignore[call-arg]