fix: regex validation not applied for custom text attributes in UI (#14110)

# Pull Request Template

## Description

This PR fixes multiple issues related to regex patterns and validation
for custom attributes.
1. Fixed regex patterns being double-escaped when saving from Add and
Edit flows
2. Fixed regex validation not being enforced in the widget pre-chat form
3. Minor UI improvements in the Add/Edit custom attribute dialog


Fixes
[CW-6625](https://linear.app/chatwoot/issue/CW-6625/bug-report-custom-attribute-regex-validation-not-working-in-ui),
https://github.com/chatwoot/chatwoot/issues/13771

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

**Loom video**

**Before**
https://www.loom.com/share/14f1983a8bc84f9fabc3663afd83cd50

**After**
https://www.loom.com/share/867c0484741140c1944fcbd43914c9c0

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/components/CustomAttribute.vue

@@ -102,13 +102,14 @@ export default {
       return this.v$.editedValue.$error;
     },
     errorMessage() {
-      if (this.v$.editedValue.url) {
+      if (this.v$.editedValue.url?.$invalid) {
         return this.$t('CUSTOM_ATTRIBUTES.VALIDATIONS.INVALID_URL');
       }
-      if (!this.v$.editedValue.regexValidation) {
-        return this.regexCue
-          ? this.regexCue
-          : this.$t('CUSTOM_ATTRIBUTES.VALIDATIONS.INVALID_INPUT');
+      if (this.v$.editedValue.regexValidation?.$invalid) {
+        return (
+          this.regexCue ||
+          this.$t('CUSTOM_ATTRIBUTES.VALIDATIONS.INVALID_INPUT')
+        );
       }
       return this.$t('CUSTOM_ATTRIBUTES.VALIDATIONS.REQUIRED');
     },
@@ -134,9 +135,12 @@ export default {
       editedValue: {
         required,
         regexValidation: value => {
-          return !(
-            this.attributeRegex && !getRegexp(this.attributeRegex).test(value)
-          );
+          if (!this.attributeRegex || !value) return true;
+          try {
+            return getRegexp(this.attributeRegex).test(value);
+          } catch {
+            return false;
+          }
         },
       },
     };