refactor: comprehensive code quality improvements

- Add logger to all exporters for consistent error handling
- Add Course.Validate() method with ValidationError type
- Create shared test fixtures in internal/testdata
- Refactor config passing: NewArticulateParser now takes *config.Config
- Add NewLoggerFromConfig() factory for logger creation
- Add context cancellation with signal handling (SIGINT/SIGTERM)
- Add godoc examples for loggers and exporters
- Add HTML exporter error path tests
- Add fuzz tests for parser and HTMLCleaner
- Fix markdown output: trim whitespace, collapse blank lines
- Remove test output files from repo

internal/services/example_test.go

@@ -5,7 +5,10 @@ import (
 	"context"
 	"fmt"
 	"log"
+	"log/slog"
+	"time"
 
+	"github.com/kjanat/articulate-parser/internal/config"
 	"github.com/kjanat/articulate-parser/internal/services"
 )
 
@@ -14,8 +17,8 @@ func ExampleNewArticulateParser() {
 	// Create a no-op logger for this example
 	logger := services.NewNoOpLogger()
 
-	// Create parser with defaults
-	parser := services.NewArticulateParser(logger, "", 0)
+	// Create parser with defaults (nil config uses defaults)
+	parser := services.NewArticulateParser(logger, nil)
 
 	fmt.Printf("Parser created: %T\n", parser)
 	// Output: Parser created: *services.ArticulateParser
@@ -26,11 +29,11 @@ func ExampleNewArticulateParser_custom() {
 	logger := services.NewNoOpLogger()
 
 	// Create parser with custom base URL and timeout
-	parser := services.NewArticulateParser(
-		logger,
-		"https://custom.articulate.com",
-		60_000_000_000, // 60 seconds in nanoseconds
-	)
+	cfg := &config.Config{
+		BaseURL:        "https://custom.articulate.com",
+		RequestTimeout: 60 * time.Second,
+	}
+	parser := services.NewArticulateParser(logger, cfg)
 
 	fmt.Printf("Parser configured: %T\n", parser)
 	// Output: Parser configured: *services.ArticulateParser
@@ -39,7 +42,7 @@ func ExampleNewArticulateParser_custom() {
 // ExampleArticulateParser_LoadCourseFromFile demonstrates loading a course from a file.
 func ExampleArticulateParser_LoadCourseFromFile() {
 	logger := services.NewNoOpLogger()
-	parser := services.NewArticulateParser(logger, "", 0)
+	parser := services.NewArticulateParser(logger, nil)
 
 	// In a real scenario, you'd have an actual file
 	// This example shows the API usage
@@ -52,7 +55,7 @@ func ExampleArticulateParser_LoadCourseFromFile() {
 // ExampleArticulateParser_FetchCourse demonstrates fetching a course from a URI.
 func ExampleArticulateParser_FetchCourse() {
 	logger := services.NewNoOpLogger()
-	parser := services.NewArticulateParser(logger, "", 0)
+	parser := services.NewArticulateParser(logger, nil)
 
 	// Create a context with timeout
 	ctx := context.Background()
@@ -64,6 +67,54 @@ func ExampleArticulateParser_FetchCourse() {
 	}
 }
 
+// ExampleNewSlogLogger demonstrates creating a JSON logger.
+func ExampleNewSlogLogger() {
+	// Create a JSON structured logger at Info level
+	// Output goes to stdout in JSON format
+	logger := services.NewSlogLogger(slog.LevelInfo)
+
+	// Logger is ready to use - calls like logger.Info("msg") output JSON
+	fmt.Printf("Logger type: %T\n", logger)
+	// Output: Logger type: *services.SlogLogger
+}
+
+// ExampleNewTextLogger demonstrates creating a human-readable text logger.
+func ExampleNewTextLogger() {
+	// Create a text logger, more readable for development
+	logger := services.NewTextLogger(slog.LevelDebug)
+
+	// Logger is ready - calls like logger.Debug("msg") output text
+	fmt.Printf("Logger type: %T\n", logger)
+	// Output: Logger type: *services.SlogLogger
+}
+
+// ExampleNewNoOpLogger demonstrates creating a no-op logger for testing.
+func ExampleNewNoOpLogger() {
+	logger := services.NewNoOpLogger()
+
+	// All log calls are silently discarded
+	logger.Debug("this won't appear")
+	logger.Info("neither will this")
+	logger.Error("or this")
+
+	fmt.Println("Logging silently completed")
+	// Output: Logging silently completed
+}
+
+// ExampleSlogLogger_With demonstrates creating a child logger with context.
+func ExampleSlogLogger_With() {
+	logger := services.NewNoOpLogger()
+
+	// Create a child logger with additional context
+	requestLogger := logger.With("request_id", "abc123", "user", "john")
+
+	// All logs from requestLogger will include request_id and user
+	requestLogger.Info("processing request")
+
+	fmt.Printf("Child logger type: %T\n", requestLogger)
+	// Output: Child logger type: *services.NoOpLogger
+}
+
 // ExampleHTMLCleaner demonstrates cleaning HTML content.
 func ExampleHTMLCleaner() {
 	cleaner := services.NewHTMLCleaner()