feat(logging): trace credential source and config path in login tool

Add diagnostic logging to the MCP login tool handler:
- Log whether username/password were provided explicitly
- If falling back to config, log the resolved config path and whether it exists
- This complements upstream scraper v0.6.18 credential diagnostics

Bumps version to 0.2.1.

server.py

@@ -265,7 +265,14 @@ async def login(
 
     mcp_logger = logging.getLogger("schwab_mcp_custom")
     mcp_logger.info("=== LOGIN TOOL CALLED ===")
-    mcp_logger.info(f"debug={debug}, username_provided={bool(username)}")
+    mcp_logger.info(f"debug={debug}, username_provided={bool(username)}, password_provided={bool(password)}")
+
+    # Diagnostic: if credentials not provided, show what config path would be used
+    if not username or not password:
+        from schwab_scraper.core.config import get_config_path
+        config_path = get_config_path()
+        config_exists = os.path.exists(config_path)
+        mcp_logger.info(f"Config fallback: path={config_path}, exists={config_exists}")
 
     with capture_logs(level=logging.DEBUG if debug else logging.INFO) as log_buf:
         mcp_logger.info("capture_logs context entered")