feat: scaffold package + report and sanitize modules (TDD)

Build order steps 1-2 of docs/PLAN.md:
- pyproject.toml (llm-ingestion-guard, stdlib-only core, extras [ml]/[judge]/[dev]), LICENSE (MIT)
- report: Finding/Report/Severity/Source shared type (pure data)
- sanitize: carrier stripping (zero-width, BIDI, Unicode-tag, HTML comment,
  data: URI) with the byte-identical / removes-only invariant
- docs/PLAN.md: v1 implementation plan (positioning A, gap-expanded scope,
  llm-security reuse map)

15 tests passing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8GmKRCdsPjWYAKWsNgeQS

tests/test_report.py

@@ -0,0 +1,61 @@
+"""Tests for the shared findings/report type (build order step 1)."""
+from llm_ingestion_guard.report import Finding, Report, Severity, Source, severity_rank
+
+
+def test_finding_defaults():
+    f = Finding(
+        label="override:ignore-previous",
+        severity=Severity.CRITICAL,
+        source=Source.INPUT,
+        detector="lexicon",
+    )
+    assert f.count == 1
+    assert f.offset is None
+    assert f.evidence is None
+    assert f.severity is Severity.CRITICAL
+    assert f.source is Source.INPUT
+
+
+def test_finding_is_frozen():
+    f = Finding(label="x", severity=Severity.LOW, source=Source.OUTPUT, detector="d")
+    try:
+        f.label = "y"  # type: ignore[misc]
+    except Exception:
+        return
+    raise AssertionError("Finding must be immutable (frozen)")
+
+
+def test_report_empty():
+    r = Report()
+    assert r.found is False
+    assert r.max_severity() is None
+    assert r.counts()[Severity.CRITICAL] == 0
+
+
+def test_report_found_and_max_severity():
+    r = Report()
+    r.add(Finding(label="a", severity=Severity.LOW, source=Source.INPUT, detector="d"))
+    r.add(Finding(label="b", severity=Severity.CRITICAL, source=Source.INPUT, detector="d"))
+    r.add(Finding(label="c", severity=Severity.HIGH, source=Source.INPUT, detector="d"))
+    assert r.found is True
+    assert r.max_severity() is Severity.CRITICAL
+
+
+def test_report_counts():
+    r = Report()
+    r.extend([
+        Finding(label="a", severity=Severity.HIGH, source=Source.INPUT, detector="d"),
+        Finding(label="b", severity=Severity.HIGH, source=Source.INPUT, detector="d"),
+        Finding(label="c", severity=Severity.LOW, source=Source.OUTPUT, detector="d"),
+    ])
+    counts = r.counts()
+    assert counts[Severity.HIGH] == 2
+    assert counts[Severity.LOW] == 1
+    assert counts[Severity.CRITICAL] == 0
+
+
+def test_severity_rank_ordering():
+    assert severity_rank(Severity.CRITICAL) > severity_rank(Severity.HIGH)
+    assert severity_rank(Severity.HIGH) > severity_rank(Severity.MEDIUM)
+    assert severity_rank(Severity.MEDIUM) > severity_rank(Severity.LOW)
+    assert severity_rank(Severity.LOW) > severity_rank(Severity.INFO)