Add JSDoc comments to various utility functions and core files.

This change adds JSDoc-style comments to several functions and classes across the codebase to improve readability and maintainability.

Comments were added to:
- `src/SEQTA.ts`: Explained the `init()` function.
- `src/seqta/utils/waitForElm.ts`: Detailed the `waitForElm()` function, its parameters, and behavior.
- `src/seqta/utils/stringToHTML.ts`: Clarified the `stringToHTML()` function, including its sanitization and styling features.
- `src/seqta/utils/delay.ts`: Added a brief explanation for the `delay()` utility.
- `src/seqta/utils/mutex.ts`: Documented the `Mutex` class and its `acquire` method (renamed from `lock`), explaining its asynchronous locking mechanism and the role of the returned unlock function.

src/SEQTA.ts

@@ -24,6 +24,19 @@ if (document.childNodes[1]) {
   init();
 }
 
+/**
+ * Initializes BetterSEQTA+ on a SEQTA page.
+ *
+ * This function performs the following steps:
+ * 1. Verifies that the current page is a SEQTA page.
+ * 2. Injects CSS styles for document loading.
+ * 3. Changes the page's favicon.
+ * 4. Initializes the extension's settings state.
+ * 5. Sets default storage if settings are not already defined.
+ * 6. Calls the main function to apply core BetterSEQTA+ modifications.
+ * 7. Initializes legacy and new plugins if the extension is enabled.
+ * 8. Logs success or error messages during initialization.
+ */
 async function init() {
   const hasSEQTATitle = document.title.includes("SEQTA Learn");