secops_mcp_list_investigations_print_to_stdout_bug

`list_investigations` uses `print()` to stdout — can corrupt MCP stdio JSON-RPC frames

`secops_mcp` 0.1.3. `secops_mcp/tools/investigation_management.py::list_investigations` writes three diagnostic messages with `print(...)` (lines 79, 86, 91) instead of routing through the module logger like every other tool in the package. On the stdio MCP transport — default for Claude Code, Cursor, gemini-cli — stdout is the JSON-RPC wire channel. Unframed writes there can be logged as malformed-frame warnings by the client or, worst case, interleave with a legitimate response and break the next parse.

Current code:

```python
print(f"Listing investigations (page_size={page_size})...")
# ...
print(f"Successfully retrieved {len(investigations)} investigation(s)")
# ...
print(error_msg)
```

The file already imports `logging` and creates `logger = logging.getLogger("secops-mcp")` at line 22. Fix:

```diff
-print(f"Listing investigations (page_size={page_size})...")
+logger.info(f"Listing investigations (page_size={page_size})...")
...
-print(f"Successfully retrieved {len(investigations)} investigation(s)")
+logger.info(f"Retrieved {len(investigations)} investigation(s)")
...
-print(error_msg)
+logger.error(error_msg, exc_info=True)
```

`grep -nH 'print(' secops_mcp/tools/*.py` to catch any others. Adding the ruff `T201` rule to CI would prevent regressions — MCP stdio servers can't tolerate ad-hoc stdout writes.