chore: Default file limits for private notes and reset attachment on mode switch (#12310)

# Pull Request Template

## Description

This PR fixes the handling of attachments and file limits in reply
modes:

* Applies **default file size and type limits** for private notes
* **Resets attachments** automatically when switching reply modes


## Type of change

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

## How Has This Been Tested?

### Loom video

https://www.loom.com/share/abad3e6a0383405ea5f31314c1494f2f?sid=38715fd0-e305-4a9b-8f4d-fc6a6e5c0833


## 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
- [ ] 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

Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/javascript/dashboard/components/widgets/conversation/ReplyBox.vue

@@ -793,6 +793,10 @@ export default {
       }, 100);
     },
     setReplyMode(mode = REPLY_EDITOR_MODES.REPLY) {
+      // Clear attachments when switching between private note and reply modes
+      // This is to prevent from breaking the upload rules
+      if (this.attachedFiles.length > 0) this.attachedFiles = [];
+
       const { can_reply: canReply } = this.currentChat;
       this.$store.dispatch('draftMessages/setReplyEditorMode', {
         mode,