fix(autocomplete): fix value persistence in DOM text widgets

Remove multiple sources of truth and async sync chains that caused
values to be lost during load/switch workflow or reload page.

Changes:
- Remove internalValue state variable from main.ts
- Update getValue/setValue to read/write DOM directly via widget.inputEl
- Remove textValue reactive ref and v-model from Vue component
- Remove serializeValue, onSetValue, and watch callbacks
- Register textarea reference on mount, clean up on unmount
- Simplify AutocompleteTextWidgetInterface

Follows ComfyUI built-in addMultilineWidget pattern:
- Single source of truth (DOM element value only)
- Direct sync (no intermediate variables or async chains)

Also adds documentation:
- docs/dom-widgets/value-persistence-best-practices.md
- docs/dom-widgets/README.md
- Update docs/dom_widget_dev_guide.md with reference

docs/dom-widgets/README.md

@@ -0,0 +1,28 @@
+# DOM Widgets Documentation
+
+Documentation for custom DOM widget development in ComfyUI LoRA Manager.
+
+## Files
+
+- **[Value Persistence Best Practices](value-persistence-best-practices.md)** - Essential guide for implementing text input DOM widgets that persist values correctly
+
+## Key Lessons
+
+### Common Anti-Patterns
+
+❌ **Don't**: Create internal state variables  
+❌ **Don't**: Use v-model for text inputs  
+❌ **Don't**: Add serializeValue, onSetValue callbacks  
+❌ **Don't**: Watch props.widget.value  
+
+### Best Practices
+
+✅ **Do**: Use DOM element as single source of truth  
+✅ **Do**: Store DOM reference on widget.inputEl  
+✅ **Do**: Direct getValue/setValue to DOM  
+✅ **Do**: Clean up reference on unmount
+
+## Related Documentation
+
+- [DOM Widget Development Guide](../dom_widget_dev_guide.md) - Comprehensive guide for building DOM widgets
+- [ComfyUI Built-in Example](../../../../code/ComfyUI_frontend/src/renderer/extensions/vueNodes/widgets/composables/useStringWidget.ts) - Reference implementation