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

.dprint.jsonc

@@ -1,42 +1,43 @@
 {
-  "typescript": {
-  },
-  "json": {
-  },
-  "markdown": {
-  },
-  "toml": {
-  },
-  "dockerfile": {
-  },
-  "oxc": {
-  },
-  "ruff": {
-  },
-  "jupyter": {
-  },
-  "malva": {
-  },
-  "markup": {
-  },
-  "yaml": {
-  },
-  "excludes": [
-    "**/node_modules",
-    "**/*-lock.json",
-  ],
-  "plugins": [
-    "https://plugins.dprint.dev/typescript-0.95.13.wasm",
-    "https://plugins.dprint.dev/json-0.21.1.wasm",
-    "https://plugins.dprint.dev/markdown-0.20.0.wasm",
-    "https://plugins.dprint.dev/toml-0.7.0.wasm",
-    "https://plugins.dprint.dev/dockerfile-0.3.3.wasm",
-    "https://plugins.dprint.dev/oxc-0.1.0.wasm",
-    "https://plugins.dprint.dev/ruff-0.6.11.wasm",
-    "https://plugins.dprint.dev/jupyter-0.2.1.wasm",
-    "https://plugins.dprint.dev/g-plane/malva-v0.15.1.wasm",
-    "https://plugins.dprint.dev/g-plane/markup_fmt-v0.25.3.wasm",
-    "https://plugins.dprint.dev/g-plane/pretty_yaml-v0.5.1.wasm",
-    "https://plugins.dprint.dev/exec-0.6.0.json@a054130d458f124f9b5c91484833828950723a5af3f8ff2bd1523bd47b83b364",
-  ],
+	"$schema": "https://dprint.dev/schemas/v0.json",
+
+	"useTabs": true,
+
+	"typescript": {},
+	"json": {},
+	"markdown": {},
+	"toml": {},
+	"dockerfile": {},
+	"oxc": {},
+	"ruff": {},
+	"jupyter": {},
+	"malva": {},
+	"markup": {},
+	"yaml": {},
+	"exec": {
+		"cwd": "${configDir}",
+		"commands": [
+			{
+				"command": "golangci-lint fmt --config .golangci.yml --color never --stdin {{file_path}}",
+				"exts": ["go"],
+				"cacheKeyFiles": [".golangci.yml"],
+				"stdin": true,
+			},
+		],
+	},
+	"excludes": ["**/node_modules", "**/*-lock.json"],
+	"plugins": [
+		"https://plugins.dprint.dev/typescript-0.95.13.wasm",
+		"https://plugins.dprint.dev/json-0.21.1.wasm",
+		"https://plugins.dprint.dev/markdown-0.20.0.wasm",
+		"https://plugins.dprint.dev/toml-0.7.0.wasm",
+		"https://plugins.dprint.dev/dockerfile-0.3.3.wasm",
+		"https://plugins.dprint.dev/oxc-0.1.0.wasm",
+		"https://plugins.dprint.dev/ruff-0.6.11.wasm",
+		"https://plugins.dprint.dev/jupyter-0.2.1.wasm",
+		"https://plugins.dprint.dev/g-plane/malva-v0.15.1.wasm",
+		"https://plugins.dprint.dev/g-plane/markup_fmt-v0.25.3.wasm",
+		"https://plugins.dprint.dev/g-plane/pretty_yaml-v0.5.1.wasm",
+		"https://plugins.dprint.dev/exec-0.6.0.json@a054130d458f124f9b5c91484833828950723a5af3f8ff2bd1523bd47b83b364",
+	],
 }