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

internal/config/config_test.go

@@ -136,6 +136,30 @@ func TestValidate(t *testing.T) {
 			},
 			wantErr: true,
 		},
+		{
+			name: "Valid output type single",
+			config: Config{
+				FileExtensions: []string{"go"},
+				OutputType:     "single",
+			},
+			wantErr: false,
+		},
+		{
+			name: "Valid output type separate",
+			config: Config{
+				FileExtensions: []string{"go"},
+				OutputType:     "separate",
+			},
+			wantErr: false,
+		},
+		{
+			name: "Invalid output type",
+			config: Config{
+				FileExtensions: []string{"go"},
+				OutputType:     "invalid",
+			},
+			wantErr: true,
+		},
 	}
 
 	for _, tt := range tests {