docs: Update skeleton loader implementation from hyperscript to JavaScript

MIGRATION SUMMARY:
- Moved skeleton loader logic from hyperscript to JavaScript (main.js)
- Changed from htmx:oobAfterSwap to htmx:afterSettle event
- Changed OOB swap from innerHTML to outerHTML for proper element replacement
- Added languageSwitching flag for state tracking
- Added 100ms delay after afterSettle for final render completion

DOCUMENTATION UPDATES:
- 2-MODERN-WEB-TECHNIQUES.md: Updated skeleton loader section with

tests/TEST-SUMMARY.md

@@ -292,11 +292,20 @@ When adding tests:
 **Philosophy**: Zero redundancy - Every test is essential and unique
 
 ### 12-skeleton-language-transitions.test.mjs
-**Purpose**: Skeleton loader display during language transitions
-- ✅ Skeleton loaders appear during language switch
-- ✅ Content replaced without full page reload
-- ✅ Skeleton removed after content loads
-- ✅ No layout shift during transition
+**Purpose**: Skeleton loader animations during language transitions
+- ✅ Component wrapper structure (dual-state: actual + skeleton content)
+- ✅ Skeleton CSS loaded (shimmer animation verified)
+- ✅ First language switch (EN → ES) - Loading class added/removed
+- ✅ Second language switch (ES → EN) - Consistent behavior
+- ✅ Third language switch (EN → ES) - Regression check
+- ✅ No stuck loading states (all containers clean after transition)
+- ✅ JavaScript event handlers configured (languageSwitching flag)
+
+**Implementation**: JavaScript event handlers in `static/js/main.js`
+- `htmx:beforeRequest` - Adds `.loading` class to page containers
+- `htmx:afterSettle` - Removes `.loading` class after swap completes (100ms delay)
+
+**Critical**: Migrated from hyperscript to JavaScript for reliable Playwright testing
 
 **Run**: `bun tests/mjs/12-skeleton-language-transitions.test.mjs`