test(identify): cover provenance branches, CLI, sparkle helper

Adds 20 tests around the new provenance path:

- identify(): local SD/ComfyUI params -> local-pipeline attribution;
  visible-sparkle gating at the 0.5 threshold (mocked detector: above,
  below, unavailable, opt-out); metadata verdict not downgraded by a
  sparkle hit; OpenAI/SynthID caveats + dedup; ProvenanceReport is
  JSON-serializable (the CLI --json path); and the honest edge where a
  C2PA manifest without an AI source marker stays 'unknown'.
- CLI 'identify': help, clean PNG, AI PNG platform, valid --json,
  missing file.
- gemini_engine.detect_sparkle_confidence: float in range for a real
  image, None for an unreadable file.

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

tests/test_cli.py

@@ -2,6 +2,7 @@
 
 from __future__ import annotations
 
+import json
 from typing import TYPE_CHECKING
 from unittest.mock import MagicMock, patch
 
@@ -243,6 +244,36 @@ class TestMetadataCommand:
         assert "stripped" in result.output
 
 
+class TestIdentifyCommand:
+    """Tests for the 'identify' subcommand."""
+
+    def test_identify_help(self, runner):
+        result = runner.invoke(main, ["identify", "--help"])
+        assert result.exit_code == 0
+
+    def test_identify_clean_png(self, runner, tmp_clean_png):
+        result = runner.invoke(main, ["identify", str(tmp_clean_png), "--no-visible"])
+        assert result.exit_code == 0
+        assert "unknown" in result.output
+
+    def test_identify_ai_png_reports_platform(self, runner, tmp_png_with_ai_metadata):
+        result = runner.invoke(main, ["identify", str(tmp_png_with_ai_metadata), "--no-visible"])
+        assert result.exit_code == 0
+        assert "AI-generated" in result.output
+        assert "Stable Diffusion" in result.output
+
+    def test_identify_json_is_valid(self, runner, tmp_png_with_ai_metadata):
+        result = runner.invoke(main, ["identify", str(tmp_png_with_ai_metadata), "--no-visible", "--json"])
+        assert result.exit_code == 0
+        payload = json.loads(result.output)
+        assert payload["is_ai_generated"] is True
+        assert payload["confidence"] == "high"
+
+    def test_identify_nonexistent_file(self, runner):
+        result = runner.invoke(main, ["identify", "/nonexistent/file.png"])
+        assert result.exit_code != 0
+
+
 class TestBatchCommand:
     """Tests for the 'batch' subcommand."""