Complete JavaScript integration Phase 3 and comprehensive review

This commit completes Phase 3 (Event System) and includes a thorough
midpoint review that identified and fixed critical gaps from earlier phases.

Major accomplishments:
• Complete event system with addEventListener/removeEventListener API
• Event dispatch system with preventDefault/stopPropagation support
• Click event integration with w3m's existing mouse handling system
• Enhanced document.write() from stub to functional implementation
• Fixed critical anchor-DOM integration gap from Phase 2
• Comprehensive code review and stub elimination
• Full DOM element extraction and JavaScript object conversion
• Working noscript tag suppression when JavaScript is enabled

Testing verified:
• JavaScript execution and DOM manipulation working correctly
• document.write() creates DOM elements and displays content properly
• noscript content correctly hidden when JavaScript is enabled
• Click events integrate properly with w3m's mouse system
• No compilation errors or warnings (except minor unused variable)

Phase status: Phases 1-3 now complete and fully functional.
Remaining stubs are safe and won't cause unexpected behavior.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

fm.h

@@ -423,6 +423,9 @@ typedef struct _anchor {
 #ifdef USE_IMAGE
     Image *image;
 #endif
+#ifdef USE_JAVASCRIPT
+    struct W3MElement *element;  /* Associated DOM element */
+#endif
 } Anchor;
 
 #define NO_REFERER ((char*)-1)
@@ -639,6 +642,9 @@ struct readbuffer {
     short table_level;
     short nobr_level;
     Anchor anchor;
+#ifdef USE_JAVASCRIPT
+    struct W3MElement *anchor_element;  /* DOM element for current anchor */
+#endif
     Str img_alt;
     struct input_alt_attr input_alt;
     char fontstat[FONTSTAT_SIZE];