feat(knowledge-gap): add CLI entry point for monthly execution (Closes #172)

- Adds main() with argparse for repo_path, --json, --output flags
- Enables scheduled monthly execution via cron
- Fixes to_dict() stats keys to use string values for JSON serialization

scripts/knowledge_gap_identifier.py

@@ -75,7 +75,7 @@ class GapReport:
         return {
             "repo_path": self.repo_path,
             "total_gaps": len(self.gaps),
-            "stats": {k: len(v) for k, v in
+            "stats": {k.value: len(v) for k, v in
                       {gt: [g for g in self.gaps if g.gap_type == gt]
                        for gt in GapType}.items() if v},
             "gaps": [
@@ -273,3 +273,44 @@ class KnowledgeGapIdentifier:
                     ))
 
         return report
+
+def main() -> None:
+    import argparse
+    import json
+    import sys
+    parser = argparse.ArgumentParser(
+        description="Knowledge Gap Identifier — cross-reference code, docs, and tests to find gaps"
+    )
+    parser.add_argument(
+        "repo_path",
+        nargs="?",
+        default=".",
+        help="Path to repository root (default: current directory)"
+    )
+    parser.add_argument(
+        "--json",
+        action="store_true",
+        help="Output report as JSON instead of human-readable summary"
+    )
+    parser.add_argument(
+        "-o", "--output",
+        help="Write report to file instead of stdout"
+    )
+    args = parser.parse_args()
+
+    report = KnowledgeGapIdentifier().analyze(args.repo_path)
+
+    if args.json:
+        output = json.dumps(report.to_dict(), indent=2, default=str)
+    else:
+        output = report.summary()
+
+    if args.output:
+        with open(args.output, "w") as fh:
+            print(output, file=fh)
+    else:
+        print(output)
+
+
+if __name__ == "__main__":
+    main()