feat: allow configuring attachment upload limit (#12835)

## Summary
- add a configurable MAXIMUM_FILE_UPLOAD_SIZE installation setting and
surface it through super admin and global config payloads
- apply the configurable limit to attachment validations and shared
upload helpers on dashboard and widget
- introduce a reusable helper with unit tests for parsing the limit and
extend attachment specs for configurability


------
[Codex
Task](https://chatgpt.com/codex/tasks/task_e_6912644786b08326bc8dee9401af6d0a)

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>

app/javascript/widget/components/ChatAttachment.vue

@@ -1,11 +1,11 @@
 <script>
 import FileUpload from 'vue-upload-component';
 import Spinner from 'shared/components/Spinner.vue';
-import { checkFileSizeLimit } from 'shared/helpers/FileHelper';
 import {
-  MAXIMUM_FILE_UPLOAD_SIZE,
-  ALLOWED_FILE_TYPES,
-} from 'shared/constants/messages';
+  checkFileSizeLimit,
+  resolveMaximumFileUploadSize,
+} from 'shared/helpers/FileHelper';
+import { ALLOWED_FILE_TYPES } from 'shared/constants/messages';
 import { BUS_EVENTS } from 'shared/constants/busEvents';
 import FluentIcon from 'shared/components/FluentIcon/Index.vue';
 import { DirectUpload } from 'activestorage';
@@ -29,7 +29,9 @@ export default {
       shouldShowFilePicker: 'appConfig/getShouldShowFilePicker',
     }),
     fileUploadSizeLimit() {
-      return MAXIMUM_FILE_UPLOAD_SIZE;
+      return resolveMaximumFileUploadSize(
+        this.globalConfig.maximumFileUploadSize
+      );
     },
     allowedFileTypes() {
       return ALLOWED_FILE_TYPES;
@@ -73,7 +75,7 @@ export default {
       }
       this.isUploading = true;
       try {
-        if (checkFileSizeLimit(file, MAXIMUM_FILE_UPLOAD_SIZE)) {
+        if (checkFileSizeLimit(file, this.fileUploadSizeLimit)) {
           const { websiteToken } = window.chatwootWebChannel;
           const upload = new DirectUpload(
             file.file,
@@ -115,7 +117,7 @@ export default {
       }
       this.isUploading = true;
       try {
-        if (checkFileSizeLimit(file, MAXIMUM_FILE_UPLOAD_SIZE)) {
+        if (checkFileSizeLimit(file, this.fileUploadSizeLimit)) {
           await this.onAttach({
             file: file.file,
             ...this.getLocalFileAttributes(file),