fix: address functionality gaps identified in code review

- Wire up --config/-f flag to actually load custom config files
  - Move config loading to PersistentPreRunE in root.go
  - Simplify main.go to just call cmd.Execute()
  - Move Playwright init to web command's PreRunE/PostRunE

- Remove unused functions from cmd/web.go (~90 lines of dead code)
  - Remove writeSingleFile, writeMultipleFiles, generateDefaultFilename
  - Remove scrapeURL, extractAndConvertContent, testExtractAndConvertContent
  - Remove unused mock function from web_test.go

- Add OutputType validation to Config.Validate()
  - Only allow "single", "separate", or empty string
  - Add test cases for valid and invalid output types

cmd/web_test.go

@@ -97,8 +97,3 @@ func TestGetFilenameFromContent(t *testing.T) {
 		}
 	}
 }
-
-// Mock functions for testing
-func mockExtractAndConvertContent(urlStr string) (string, error) {
-	return "Mocked content for " + urlStr, nil
-}