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)

.idea/.gitignore

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+# Default ignored files
+/shelf/
+/workspace.xml
+# Editor-based HTTP Client requests
+/httpRequests/
+# Datasource local storage ignored files
+/dataSources/
+/dataSources.local.xml

.idea/modules.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="ProjectModuleManager">
+    <modules>
+      <module fileurl="file://$PROJECT_DIR$/.idea/x-editable-bs5.iml" filepath="$PROJECT_DIR$/.idea/x-editable-bs5.iml" />
+    </modules>
+  </component>
+</project>

.idea/php.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="MessDetectorOptionsConfiguration">
+    <option name="transferred" value="true" />
+  </component>
+  <component name="PHPCSFixerOptionsConfiguration">
+    <option name="transferred" value="true" />
+  </component>
+  <component name="PHPCodeSnifferOptionsConfiguration">
+    <option name="highlightLevel" value="WARNING" />
+    <option name="transferred" value="true" />
+  </component>
+  <component name="PhpStanOptionsConfiguration">
+    <option name="transferred" value="true" />
+  </component>
+  <component name="PsalmOptionsConfiguration">
+    <option name="transferred" value="true" />
+  </component>
+</project>

.idea/vcs.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>

.idea/x-editable-bs5.iml

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+<?xml version="1.0" encoding="UTF-8"?>
+<module type="WEB_MODULE" version="4">
+  <component name="NewModuleRootManager">
+    <content url="file://$MODULE_DIR$" />
+    <orderEntry type="inheritedJdk" />
+    <orderEntry type="sourceFolder" forTests="false" />
+  </component>
+</module>