Modernize Select2 integration and fix popover page jumping

- Upgraded Select2 from bundled v3.4.4 (2013) to v4.x peer dependency
- Removed legacy Select2 v3.x bundled files from lib directory
- Updated Select2 input to use v4.x API (events, AJAX, templates)
- Fixed Bootstrap 5 popover page jumping issue with multi-timeout scroll restoration
- Added comprehensive migration documentation in README-select2-upgrade.md
- Rebuilt all distribution files with updated source code

Breaking Changes:
- Select2 now requires separate installation as peer dependency
- AJAX configuration updated for v4.x format
- Event names changed (select2:select vs select2-loaded)
- Template functions renamed (templateResult vs formatResult)

README-select2-upgrade.md

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+# Select2 Modernization
+
+This fork has been updated to work with **Select2 v4.x** instead of the bundled v3.4.4 from 2013.
+
+## Breaking Changes
+
+### Select2 Dependency
+Select2 is now a **peer dependency** and must be installed separately:
+
+```bash
+npm install select2@^4.0.0
+```
+
+### Include Select2 in Your HTML
+You must now include Select2 yourself:
+
+```html
+<link href="node_modules/select2/dist/css/select2.css" rel="stylesheet" type="text/css">
+<script src="node_modules/select2/dist/js/select2.js"></script>
+```
+
+For Bootstrap 5 styling, also include:
+```html
+<link href="https://cdn.jsdelivr.net/npm/select2-bootstrap-5-theme@1.3.0/dist/select2-bootstrap-5-theme.min.css" rel="stylesheet">
+```
+
+## API Changes
+
+### Event Handling
+Select2 v4.x uses different event names:
+- `select2:select` instead of `select2-loaded`
+- `select2:unselect` for deselection
+
+### AJAX Configuration
+For remote data sources, use the new v4.x format:
+
+```javascript
+$('#element').editable({
+    select2: {
+        ajax: {
+            url: '/api/data',
+            dataType: 'json',
+            delay: 250,
+            data: function (params) {
+                return {
+                    query: params.term,
+                    page: params.page
+                };
+            },
+            processResults: function (data) {
+                return {
+                    results: data.map(function(item) {
+                        return {
+                            id: item.id,
+                            text: item.name
+                        };
+                    })
+                };
+            }
+        }
+    }
+});
+```
+
+### Template Functions
+Use `templateResult` and `templateSelection` instead of `formatResult` and `formatSelection`:
+
+```javascript
+select2: {
+    templateResult: function(item) {
+        return item.text;
+    },
+    templateSelection: function(item) {
+        return item.text;
+    }
+}
+```
+
+## Migration Guide
+
+1. **Install Select2 v4.x** as a peer dependency
+2. **Include Select2 CSS/JS** in your HTML before x-editable
+3. **Update AJAX configurations** to use v4.x format
+4. **Update template functions** to use new naming
+5. **Test thoroughly** - Select2 v4.x has different behavior
+
+## Debug Mode
+
+The updated code includes console logging for debugging. Check browser console for:
+- `[Select2 Debug] value2input called with: ...`
+- `[Select2 Debug] Item selected: ...`
+- `[Select2 Debug] Change event triggered: ...`